yeah, McKenna CM is really for younger kids, unless yours likes train tracks and a mini grocery store with little carts to push around. The SA CM is a little more interactive, but it will take your kids 30 mins to go through it and they'll be done.
Look into tubing down the river. That is AWESOME (not exactly white rapids but nice and relaxing). Get a cooler tube where you can put drinks and snacks in it (or you can do the white trash thing and bungee cord a cooler to a regular tube lol).
You can't go wrong with Country Inn & Suites or Hampton Inn for nice rooms and excellent breakfasts but San Marcos/New Braunsfels has some great B&Bs. We stayed in a few but for the life of me I can't think of the names only bc I wasn't the one who booked them or drove to them. There is one house for rent right off the river in NB that slept 17 of us...there were 4 families and we each got our own rooms and a HUGE living area with an attached screened in porch. I think the property has smaller homes but that one we stayed in was NICE.
There are tons of hiking trails in that area - really beautiful walks because its in the hill country (my most favorite part of Texas :) ) Have fun ya'll!