Take a look at the Horseshoe Bay Marriott on Lake LBJ. We stayed there during the 4th last year. They had lots of activities for the kids, an 18 hole putting green putt putt course, 3 swimming pools and even access to a small portion of sandy "beach" at the lake.
Within driving distance you can get to Austin, Fredericksburg and Luckenbach. We went towards Fredericksburg and stopped in Johnson City to see the boyhood home of Pres. LBJ and then stopped at his ranch for a tour of the home land/home, Texas White House, that where he lived during and after the presidency. We did a bit of shopping in Fredericksburg and in Marble Falls also.