This will be our first overseas trip since the birth of our daughter, who is approaching 4.5 years old and after battling with severe PND, I have finally worked up enough courage to try adventuring again.....our last trip to the US was in 2008 and we loved every minute of it. This time we won't have as much free time...perhaps 4 weeks only and travelling probably from October to November...
I am looking for any suggestions.....we missed out last time on Lake Tahoe, Niagara, Yellowstone NP and Hawaii....however, I am completely open to any ideas you can share with me that are both friendly enough for a very sociable and easy to travel with child and adventurous enough for a fit and active father!

Again you are assuming that people know what PND is or are willing to look it up to help you.

Start with a stopover in Hawaii on your way to the west coast. Lots to see and do on Oahu while dealing with jet lag.

Then begin looking at places in California that call to you; Yosemite should definitely be on the list, along with Lake Tahoe. For more adventuring, there's the Big Sur area, on your way to southern California, where I think all of you would enjoy the San Diego Zoo and Wildlife Park (different locations).

I know what PND is, but the OP wasn't asking for help with that, just ideas about where to visit.

Uh, where are you going? The US or Europe? You have threads for both.

And the main question is whether you can hang with the active dad with your lung issues. If you have issues with getting enough oxygen in your blood, then you may want to limit mountain destinations.

California will have a balance of all adventure and kid attractions that you need. It'd help if you said where you went last time . . .

First, how are you planning to "travel" around the US during your visit - rental car, airplane, a combination of both???? The US is a big country - land mass wise it's some 2 million sq. kilometers larger than Australia and it has some 293 million more people. That means there's a lot of places to see and it's virtually impossible to see it all in 4 weeks. You can only scratch the surface.

Second, you obviously have to fly to Hawaii so if you decide to make that part of your itinerary I'd make that either your first or last stop.

Third, the other destinations you mentioned in your post are fairly far apart. Lake Tahoe is the western most of your continental US destinations, from there it's about about 750 miles to Yellowstone NP. Niagara Falls is another 2,000+ miles from Yellowstone. So you probably want to fly if you plan on visiting all those places.

Fourth, October and November is mid-Autumn in the US so the further north you are in the country and the later in November you travel the cooler it will be. Yellowstone NP has only limited "services" and some access roads and sections of the park are closed in October and November. Conversely, the southern part of the country will generally have milder weather.

It would help if you told us where you visited during your previous trip, what you liked and disliked about that trip and whether or not you'd like to return to any of those destinations or experience completely new places during this trip. That way you won't get suggestions you've seen before or just aren't interested in seeing.

Also, let us know if you prefer to visit larger cities, more country-like settings or perhaps a combination of both (if both which is your primary objection and which would be secondary).

Do you want to include stops at theme parks like Disneyland, Walt Disney World that might appeal more to your child than to the adults?

With only 4 weeks, I'd choose one general area of the country, such as the west coast, New England, the mid-Atlantic states or the south east coast and spend your time driving between some of the different cities & towns in that particular area. You can plan an itinerary where you stay 3 or 4 nights in each location then drive maybe 4 to 5 hours to your next stop. This way you won't be spending all your time driving and you'll be able to see the sights "along the way and still have plenty of time to explore the general towns and cities you'll be visiting.

Post Nasal Drip?

I think PND refers to postnatal depression.

I thought so too, but based on an above post, I think it's a lung thing.

My choice would be New England/east coast. Pick a few laid back places to enjoy, like outer banks or cape cod. All the towns are so close together and because of the train service, you could limit your driving to rural destinations. I saw a lot of kids on Cape Cod, but there's also a lot of outdoor activities for your hubby. California would be another option- Yosemite is one of the few nps that I can think of that has amenities. Santa Barbara or somewhere similar would also work. Gold country would be great, but may be more driving than you want to do. Vancouver, BC and Vancouver Island are also options.

I think it's the breathing disorder implied by BigRuss in his response: Paroxysmal nocturnal dyspnoea

Never mind. I just saw the October part. I'd probably focus on the south. Scratch Tahoe and Vancouver as well probably.

Are mountains or even just high altitudes a possibility (much of the west is one or the other)? And late Oct to Nov will start to get you into cold or even wintry weather ins some places (I landed in Denver once on 9/9 and it was into 6" of snow).