San Marco is just north of San Antonio on I-35.

When in Glen Rose you should consider Dinosaur Valley State Park. Glen Rose is the dino capital of Texas. http://www.tpwd.state.tx.us/state-parks/dinosaur-valley

You'll be in the Hill Country during wildflower season. That itinerary could write itself.

And there's this: http://www.texasoutside.com/texas_zip_lines/index.html

For Dallas, the Sixth Floor Museum is the one all the tourists seem to invade (lived here 17 years, never visited). This year on 11-22-13 it will be the 50th anniversary of JFK's assassination.

The Dallas Arts District has various art museums: DMA (general art), Nasher (sculpture), Crow (Asian art). The Perot Science Center exhibits what its name implies - it's in a hideous building on the west side near downtown but is very good and especially so for kids who are 8 and older.

You'll get a lot of Austin lovers on this board, but if you're just going to drive by, do it in the most swift way possible. You won't really get much of a vibe from it just on a drive through (you'll be almost close enough to go there for dinner from your hotel - just take the loop roads out of San Antonio and I-35 to Austin). Austin and Travis County are a microcosm of LA culturally and, like Southern California, the traffic is horrendous.

You'll pass San Marcos on I-35, but if you really want to do Natural Bridge Caverns, I'd drive right on by. It is humongous...and exhausting shopping. Natural Bridge Caverns is just a bit further down the road and is a lot of fun for all ages. If you want mall shopping, your hotel isn't that far from San Antonio's nicest mall, La Cantera.

Late March will still be too cool for tubing for most people, but your hotel has the heated "Lazy River" where you float along on tubes through a portion of the property and its very pretty landscaping. I'd skip Austin for dinner unless you relish an hour and a half drive each way and you just enjoy driving I-35. LOL (You'll see what I mean when you drive it! . ) I think you'll enjoy the Segway tour. It takes you into my very favorite section of San Antonio, the historic King William district.

You will be in Texas at a beautiful time of year. Bluebonnets are just about peak then and you can easily do some Hill Country drives from your hotel. One of my favorite Bluebonnet drives is the Wilow Coty Loop outside of Fredericksburg. Gorgeous, but don't attempt it on a weekend as crowds then can be heavy.

We used to live in Plano. Basically, it's a bedroom suburb for Dallas. Dallas, by the way has fabulous shopping! You might get your fill there. The one former tourist draw in Plano was Southfork ranch, setting for the Ewing ranch in the TV series, "Dallas". I think it's function space now, and as in former years, this is a drive by only most likely, but you can see the house very well from the road.

You will probably be in Dallas for "Dallas Blooms" at the Arboretum . These beautiful gardens on extensive grounds along White Rock Lake are planted for a spectacular spring show. Once again, if possible, go on a weekday. It can get very crowded during Dallas Blooms, but its really beautiful!

You've got a full itinerary but I really like it! You've put a lot of thought into your trip, for sure. Hope you enjoy it and have perfect weather. That really is one of the nicest times to be in TX!

Uh oh, typo. It's the Willow City Loop, not 'Coty'!

I'm thinking it will still be to cool for tubing at that time. Perhaps I am wrong.

Thanks for your replies. It's all really helpful advice. It sounds like we would be better to bin the idea of tubing down the river and do the Willow City loop that afternoon instead. Hopefully as it will be mid week it won't be too busy. The Perot Science centre in Dallas looks great as well. Please do feel free to add any other suggestions. We'll probably only ever come to Texas this once so I really want to go home feeling that we have enjoyed a real Texan experience.

www.dwazoo.com

Dallas World Aquarium is AWESOME. Downtown Dallas not far from the 6th floor. Indoor rain forest with animals and every fish you think of.

I highly recommend the Dallas Arboretum, also. It's expansive and beautifully done.

Knowing the ages of your daughters, I'm not sure they'd want to spend a lot of time in the Sixth Floor Museum, but just a short hop away is the Dallas World Aquarium. Every person I've ever taken here (adults, teens, kids) LOVED it. I love it too. It is not just an aquarium, but also houses a host of rain forest creatures. Don't miss the amazing seahorses, the spotted garden eels and the very cool shark tank!

The cost seems steep, but trust me- you'll get your money's worth. Plan on spending a minimum of 2 hours. Do check out the website: http://www.dwazoo.com/

PS. Do not confuse the DWA with the Dallas Zoo.
PPS. Go early- it is an indoor rain forest and steams up with the sun.
PPPS. Here is a great youtube video someone did of the DWA http://www.youtube.com/watch?v=IVor82jtjIE

Definitely too cold to tube (or is it toob?).

Plenty of shopping in Plano, Frisco and Dallas. There is an outlet mall in Allen too.

http://www.premiumoutlets.com/outlets/outlet.asp?id=5

Here is a link to a gun range in Dallas. I know nothing about it other than it exists.

http://www.elmfork.com/

Just a thought about shopping. (Incidentally, shopping is claimed to be the number one source of tourism in Texas; at least by outlet mall management.) If you go to any of the premium outlet malls, be certain to stop by the customer relations office. Nearly all of the malls offer complimentary coupon books to international travelers. Many also have a tax refund office that will instantly refund any taxes applied to your receipts. If the mall you shop at does not have such an office, you can get a refund for all taxes at the tax refund office in the Grand Prairie mall about 1/2 hour south of the DFW airport.