We had a great time last year at Guadalupe River Ranch.
http://www.guadaluperiverranch.com/
It's in the hill country. They have a few larger cabins that would hold your whole family. We actually got a room with one bed and brought along an inflatable sleeping bag thing for our daughter (3 yrs at the time), and the baby (1 yr) slept in a pack-n-play.
It really was a fun time for everyone. There is a pool, sand volley ball pit (read: giant sandbox for younger kids) and little park area, horse riding (even a short corral ride for the little ones), covered wagon rides, a short walk to the river for splashing fun, nightly Smores roasting. You can rent a bicycle (for free) to cruise around the ranch. There's an onsite restaurant, an onsite shop with snacks and treats, spectacular views everywhere, deer roaming around. We requested a fridge in the room and we packed sandwiches and breakfast food. It was nice to eat on the patio/balcony at our room.
It's just 30 minutes from Lukenbach, which was a fun little stop on the drive down. If there's an event there, the consession stand has snacks, drinks and dinner.