I'm a single mom and took my kids this past July. But, my kids were 8 and 3. Sea World doesn't open until 10, I think (kind of late). So, we would get there first thing and then stay until about 1PM. Then, we went back to the hotel where the youngest and I took a nap. The older one played on his nintendo while we napped. Then, in the afternoon we would play at the hotel pool and then by the evening, we would go back to Sea World for a little while.
It's hard at that age because of the naps, but we took it easy. However, at the time that we went, the pass to get you into Sea World also got you into the water park. NOW, that has changed. You have to pay separately for the water park and sea world. You may really want to look into how much that will cost you because we actually went to the water park two mornings and then did Sea World in the evening - all on the same pass.
The other advice I can give you - we had some kind of pass. I don't remember what kind. But, when we arrived in San Antonio, it was about 4PM. We decided to go on over to Sea World and we went in the gates through the turnstile. There was absolutely no lines. Well, what no one told me (not even the agents there) is that to get in the next day, you have to register the passes at a window agent. We could have easily have done that at the window the evening we arrived (no lines). But, the next day when we went, we waited in the lines to go through the turnstile, which was a NO GO and the turnstile person directed us to the window - where we had to wait in line all over again. We were probably in lines for over an hour that morning. Miserable!
Also, I rented a stroller from Sea World so that I would not have to mess with carrying a stroller around. I highly recommend this. I also took a colored laminated sheet and ziptied it to my stroller so that my Sea World stroller was easily identifiable from ALL the strollers that were parked outside of the shows.
Good luck!
L.