I've done Disney/Seaworld/Universal several times now. When the kids were young (ie under 10) we stayed on site. Its much easier than trying to stay off property. Its too much for little ones to spend the whole day in the park. We found they did best by getting up early and going to the park, coming back to the hotel around one for lunch, a swim and a rest and then going back at night.
Once they were older we started to stay off property. We like Sierra Suites as they run packages and specials. The last time we were there it was $99/per night for a family of six. Because we stayed two nights we got 2 free tickets to Universal which brought the cost down to about $50 per night. They also offered a free continental breakfast and free transportation to the attractions (the bus ran to and from a certain times).
If you have any questions feel free to email me.