The Hoppin' House in Lakeway is great. It has several bounce house-type play structures, including one that is a ball pit, and a big pit full of foam blocks. A couple are good for younger kids, too. My 2 1/2 year old had a great time, even on the big slides (with me!). It's only $5 per kid for the whole day because you can get a wristband so you can leave and come back. They also have a cafe-type area where you can have snacks, which they have available to buy, or you can bring your own. There is also a little room with a big table for birthday parties. It's on 620 south by the Randall's at Lohman's Crossing--enter the driveway for the Valero gas station and Chicken Express, and go in between them to the back.