We had a blast at Smith Lake in Vidor, Tx.
This place had a 23 acre lake with a huge roped off sandy beach for the kids and a larger roped off area for the deeper swimming area. The lake also had a 2 tier jumping platform (15' & 30') plus a zip line that spanned across the lake. There was a floating pier in the middle of the lake. The lake had covered tables with BBQ pits, restrooms with showers, a snack bar, and float rentals. One nice thing was that Alcohol is not allowed. The other cool thing about this large lake is that you can fish the rest of it which is the majority of the lake. Plenty to do here. Think I am going back!
Admission is only $7 per person.