Am I correct in thinking that you plan NO time for visiting Washington DC itself? If that is the case -- that you plan to immediately leave DC and head for Shenandoah -- then two weeks for your entire trip would be about right.

Just two warnings, and both have to do with your choice of August to visit:
1) Weather will be stifling except right on the beach or in the mountains. I don't know if you're familiar with summers in the Southeast U.S., but they are NOT as pleasant as those in the U.K. In particular, Washington DC is NOT a place to be in at this time -- which is why I'm hoping you WON'T.
2) August is the high point for travel in the U.S. As such, beaches and mountains -- the two places you'll be heading for in order to escape the heat -- will be JAMMED. Try to have reservations at least a couple days in advance for each day you travel; otherwise you'll end up spending an hour or so each night hoping to find an over-priced flea-bag motel. Don't show up at a campground in Shenandoah on a late Friday afternoon and expect to find an isolated spot for camping!

Shenandoah is one of my favorite spots to visit -- I've made multiple trips over the years -- so feel free to contact me with any questions you might have.

I'd go so far as to say make reservations well before your trip. Getting a hotel in DC or Raleigh, if you need them, shouldn't be a big deal, but any vacation destination in August will be quite busy. However, at the end of August a lot of US schools will have started back, so that will help a bit. (Actually, if there's any way you can bump your trip back to early/mid-September, that would be even better - the first Monday of September is Labor Day here, and is usually the dividing line between "high season" and "low season" prices for things like beach rentals. Plus just about every school will be back in session then, so there will be fewer families on holiday. Not sure when school will start for you in the UK, though.)

The weather in the cities will likely be quite hot and humid - it wouldn't be shocking to see 90 or 95 degrees Fahrenheit with 90% humidity. However, the mountains should be cooler and less humid, and at the beach it'll be a tad better than inland, so it's good that you plan to do those. (Plus any indoor area will be air conditioned until frigid.) I don't know that the Smokies are all that different from the Shenandoah Valley (I've actually not been to that part of Virginia), but there are some great hikes and things to do in the Smokies. Cades Cove near Townsend, TN is one of the most popular attractions. Gatlinburg might be fun for your six-year-old, but could be mobbed that time of year. Most people on Fodor's think it's a huge tourist trap, but it does have most of the restaurants and attractions on the Tennessee side of the Smokies.

Thank you both, PaulRabe & jent103, very much for your replies. Unfortunately we are having to combine our trip with the kids summer school holidays both in the UK and US, so we have no flexibility to change when we visit. We are restricted to visiting between 20/8 - 3/9, so it would seem we will have to contend with the heat & humidity (and crowds!) It sounds like its sensible advice to get accommodation booked up early in the Nat Park and at the coast, I assume any stop gaps in between will be slightly easier to get booked once we are there?
We weren't busting to visit Washington DC itself and if the city is as bad as you say in August, we will probably take your advice and avoid spending any time there.
Is it necessary to actually stay within Shenandoah or could we stay outside and travel in? Is the Skyline route easily accessible from outside of the NP?
Also, I'm having trouble gaging the scale of the Outer Banks area - are there any particular places that are a definite to visit in this area?

You can stay outside of the park when you visit Shenandoah NP, but then you've got somewhat of a drive each day to get in and out of the park. I would recommend staying in one of the lodges, Skyland or my favorite, Big Meadow, at least part of the time. Each has a number of lodging options so you should be able to find something that suits your family.

Washington D.C. is pretty hot and humid in August, but it does have lots of great (and free) museums and memorials. I would plan on at least one full day here to see some of the city at the beginning or end of your trip.

One place at the Outer Banks that I would plan to visit is Kill Devil Hills, North Carolina. This is the site of the Wright Brothers' first flight and the Wright Brothers National Park is well worth a visit. Also, if either of you would like to give hang gliding a try, you can do that at nearby Jockey's Ridge State Park. We arranged our hang gliding lesson through Kitty Hawk Kites.

> Is the Skyline route easily accessible from outside of the NP?

There are several entrance stations where you can easily go from a US Hiway onto Skyline Drive, but there is no way to get onto that road without going inside the NP. In order to drive on Skyline Drive, you must pay the entrance fee -- period.

I highly recommend the obvious entrance -- just south of Front Royal, which is just off Interstate 66 and about 72 miles (115 km) from Washington DC.

The Outer Banks is a string of very skinny barrier islands, something like 200 miles long according to Wikipedia. I had to look that up, because I've never been to the far southern end, myself.

While it's been 10 years since I last visited, I have always enjoyed the northern bits of the Outer Banks -- Duck & Corolla, specifically. They are less developed than Nags Head, & you can still visit the Wright brothers' site at Kill Devil Hills for an afternoon. Be aware, though, that places like Duck run heavily to big big beach houses rather than hotels, or even rental condos. Your lodging options will depend on just how many people you are housing.

I wouldn't go as far as the Outer Banks. You are covering a lot of ground before you get to Raleigh, and actually only have about 3 after Raleigh to get back to Washington. The "good" part of the last of August may be that school is largely back in session in the South, so the beach trips are over for families.
There are beautiful beaches closer than OBX and easier to access.

If you can I sure would try to make it to the Smoky Mountains. The North Carolina side of the park is beautiful. It may be crowded that time of year but there are places to get away from it and enjoy the wonder if it all.
Deep Creek at Bryson City has some great camping and Rock Creek Cabins there are very nice, their Abbot Cabin has some of the most beautiful views of the mountains I've seen.

Agree with jilomi about the Bryson City side of teh Park.
To put the Outer Banks in perspective for the Smokies, it is probably at least a 12 hour drive from Bryson City to OBX.

Can't help with the Smokies until after we go in April ... we plan to explore the park from Townsend, TN though, so it might not be the area of your focus. I'll be posting to my blog ... if you'd like to check it in May for some of the things we did, here's the link: http://2totravelphaeton.blogspot.com/.

DC -- we live about 14 miles from DC; agree that it is hot, humid, and miserable in August. However, if you've never been and you're coming all the way from the UK, I'd plan a day in the city ... there are a lot of museums that are free, several of which could be fun for a 6 year old (Natural History Museum and Air and Space being two of them).

Skyline Drive is accessible from several entrances, and yes, you can stay outside the park, but it is a haul to get in and out. I'd stay at either Skyland or Big Meadow lodges ... we always ask for one of the renovated rooms. Take the drive slowly and enjoy the overlooks. The scenery might be a bit hazy with the summer heat. Early morning and early evening is a good time to see deer in the Big Meadow area. We've seen black bears in that area as well. I have some of my photos from our visits at this link: http://eenusa.smugmug.com/Day-Trips-Weekend-Getaways/Virginia. It will be cooler in the park, but the humidity can still be a factor.

OBX -- we were there last April, in our motorhome. I hear it gets really crowded in the summer, but there are a lot of fun things to do ... if you decide to keep it in your plans, and would like to check out my posts ... here's the link: http://2totravelphaeton.blogspot.com/2011/04/nc-obx-trip-in-spotlight-monument-to.html ... all of the OBX posts are in the April 2011 archive. The sand dunes at Jockey's Ridge would probably be fun for your 6-year old as would the ponies of Ocracoke, and of course just beach time would be good. The Wrights Brothers National Park is a great place, though I'd probably skip the presentation in the visitor center since it is long.

Have a terrific visit.

I agree with eenusa. I would at least spend a day or two in DC if you have never visited it before. The Smithsonian museums are all inside and I could spend a week looking at them. Maybe a quick stop or drive by of some of the monuments.

Smokys and Shenandoah are somewhat similar in appearance. Right outside the Smokys is Gatlinburg, which has a lot of fun stuff for a kid to do. I would probably just go with Shenandoah unless Gatlinburg was something you really wanted to do. Again, expect that place to be crowded too.
Shenandoah has some hikes to swimming holes and waterfalls that you could get in a bit to stay cool. Now Gatlinburg is highly commercialized and not really what I consider a National Park setting. Very very busy.

We are staying at Lewis Mountain Cabins at the end of May, which is different than Skyland or Big Meadows. I haven't stayed there before, so can't tell you much about it, other than it is more primitive than Big Meadows or Skyland. Luray Caverns might be a place you want to visit too. They are just outside the park.

I hate to be the one to bring this up, but August and September are high hurricane months. Just make an alternate plan for what you want to do in case you can't visit the Banks, or you have to evacuate.

Voice of reason, that!! And I'm not sure everything will be put back in place from last year. I will say again, it is far to go. it isn't the only part of the NC coast OR even Maryland, that is pretty--and somewhat closer. If you want some "wildish" coast, look at Chincoteague in Maryland. It could be "on your way".

As a person who has spent many summers on the beaches of the Outer Banks IMO those wild areas such as Chincoteague in Maryland are fine but it does NOT compare to the Outer Banks and the many things you can do there.

Furthermore, depending on exactly what you want out of the beach segment, you might consider going further south than Duck, Corolla, or even Nags Head. The towns further south such as Waves, Avon, and Hatteras Village itself might be more to your liking as might be the island of Ocracoke.

As to the heat and humidity, believe me, it will be hot and humid at the beach, too.

It will all be lots of driving! I have lived in Va all my life with the exception of 10 years in the Raleigh area. My most favorite place is the Outer Banks, the southern Outer Banks in particular (less development, best waves and windsurfing).

A really scenic trip from Raleigh would be driving either to Swanquarter or Cedar Island, taking a ferry to Ocracoke Island, stay one night there, walk around the village, see the lighthouse, then drive to the other end of the island (stop to see the wild ponies) and on to the ferry (this one is free, not sure of the other 2) to Hatteras. Head north, climb the Hatteras lighthouse, play on the beach there or stop whenever you want to check out the beach, see the windsurfers at the Canadian Hole (if its windy). You will go through several small villages, and lots of undeveloped beach and marsh. If you have 4 wheel drive SUV, drive on the beach some. After Oregon Inlet (big bridge connecting 2 of the island) and before the end of the park there is a lifeguarded beach area (ocean side of Bodie Island visitors center) with bathrooms and showers (cold water). You can stay at Kill Devil Hills, Nags Head or Kitty Hawk (lots of hotels and restaurants there). Climb the giant sand dune, and play some more on the beach. Then head north and then east on Rt. 158 back up to DC.
Many of the hotels have 2 or 3 night minimums in the summer and reservations are a must, so need to check on that. Midweek visit might help. Also, the water can be rough so be careful! The unspoiled scenery is beautiful but it is a long drive.

For the mountains part of your trip, you probably would not want to try to drive the entire Skyline Drive/Blue Ridge parkway. It's slow going and everything starts to look the same after a few hours. I think the Skyline Drive portion has a fee, Blue Ridge Parkway is free. It turns into BR Pkwy when it crosses Rt. 64 (near Charlottesville, VA).
I also agree that the Smokies area and Shenandoah are similar enough you don't need to see both.
You should try to read up on the areas of Shen NP and BR Pkwy and based on where you can get lodging, drive the Parkway in that area, but use some highways to get there.
I think the BR Pkwy goes through more rugged mountains but I've just been in that area more for camping and hiking. Not as familiar with the Skyline Drive area.

As for DC, you can take a hop on/hop off bus one day to get the highlights. There is no fee at any of the Smithsonian Museums so you can pop in and out for how ever long you want.