Sounds strikimgly similar to our spring break last year... Ours were 5 and 3, and we went with 2 other families (a total of 6 kids ages 3-7 vs 6 adults). Some highlights/suggestions:
- Stopped in Monahans for a night on the way out, and the sand dunes were a big hit.
- Stayed in RVs/trailers in an RV park in Terlingua. We thought it was a good home base. If you've never been, you should know it's BIG Bend, so plan to drive. A lot. Don't expect to see the entire park in a single trip.
- We hiked Santa Elena Canyon. Very manageable with our kiddos, and even my 3yo hiked this one. You'll need to pack/carry the 1yo, of course.
- Hot Springs were the highlight of the trip. Jumped into the RG and floated down a few hundred yards ( there's a weathered "takeout" on the US side and trail back to the springs. We also had life jackets for the kiddos, even though they can all swim. The RG had a bit of pace to her flow, be safe. But it was a BLAST.
- We hiked another trail, trailhead was off the road into the basin, maybe Lost Mine Trail? Reasonable elevation gain to a nice view (into Mexico, IIRC). All kids except my 3yo had plenty of legs to get to the top and back. We just let the little guy climb as long as he could, then tossed him onto my back(pack). Start early, it will get crowded. Bring snacks and water, pack lunches for the car and picnic after decending.
- Dinner at Starlight. Go early, there will be a wait, probably a long one. We showed up at 500, put our name on the list, and had time to go back to the RV park and shower everyone.
Have fun!