W.C.
I'm new to SA (from the midwest), so I'm a little uneducated. Why do you need sun protection tents at the beach? I have a 3year old and have always just used 50sunblock every hour or so and sun protection clothing/hats. Is that not enough?
We took our three year old tubing. She is huge though (most people guess she is 4 or 5) and we have a life jacket on her and she rides on dad's lap, but she loves that. We run the horseshoe twice and that is just about the length of her attention span. There are some good camping ares around there also.
We love Sea World. There aren't many rides, but the lines are short enought that Dh and DS could go while you wait- though he might be too short for some of them. There are also several sand boxes to play in. The water park has a great kiddy area too.
My daughter loves the River Walk. She especially enjoys the gardens and the ducks. She always finds new bugs and creatures and we get to enjoy the scenery.
Canyon Lake has boats to rent and primitive cabins also. There are also tent camping spots that are great. We love Canyon Lake.
Port Aransas has a great little B&B. We haven't made it there yet, but it sure looks like fun. I have heard great reviews They have a coastal blend package that includes dinner and tickets to several attractions. I can't wait to try this out. Here is the website.
http://www.plantationsuites.com/specials-coastalbend.htm
Hyatt has a wonderful resort in San Antonio (not the hotels- a resort) also with a lazy river and all kinds of things to do. Again, we have not yet visited, but we are owners in Key West and Hyatt is just fantastic and so family friendly!
We have only been in SA since Feb, but we have yet to get bord. I am typing this from Indiana while visiting family and I have forgotten how spoiled we are down south. There is nothing to do here.