S.H.
K.,
San Antonio is my hometown. :D My husband is in the hotel business and says to try these hotels; although, they may be booked already:
Red Roof Riverwalk
StayBridge Suites Downtown
Best Western Sunset Suites
Hyatt Place Riverwalk
Yes, you will need two days for Sea World and Fiesta Texas. They both have water parks, but I don't know if they are open yet. If you don't want to pay the parking at Fiesta Texas, you can park at the shopping area across the highway and walk across the parking lot. Although, you may be so tired afterward, you may want to just park at the park. At Sea World, you HAVE to see the Viva Shamu Show. It is wonderful! Be sure to have your video/digital camera ready for some great night shots! I'd leave an ice chest in the car to go to at lunch. The food can be quite pricey for a family, and the lines can be really long, especially when you're hungry.
As far as restaurants, I do recommend Mi Tierra and La Margarita, but I've always had to wait; so, go early. There is another great restaurant Downtown called Las Piedras Negras. You'll have to drive to it, as it's not at the Riverwalk. There's a Rainforest Cafe on the Riverwalk, and if you can get to one, go to Chris Madrid's for a yummy burger.
There's an IMAX theater at the River Center Mall. The Children's Museum is really fun. My kids didn't want to leave, and the staff didn't rush them at closing time. They have so much for kids to do (without reading...lol), and it is right near the Alamo.
Anyway, I will let you know if I think of anything else. Have a great time!
-------By the way, when you're at Sea World, you might want to visit "Rudy's" (BBQ) across from Sea World. Delicious!