If you want a beach day skip st Augustine and do Clearwater instead. Make a point of going on the big yellow speedboat...they make a real point of getting there dolphin and if you take the ride early on the day..ie either 12 or 2 clock and you don't see a dolphin then you ride for free in the next trip out. If you're only there for a short time I'd skip the space centre too. I love gator land , but that's because we like a walk along the boardwalk to watch the birds nesting and the alligators congregating underneath hoping for something to fall into their hungry mouths.
The clearwater pier 60 at night is great as is watching the pelicans dive for fish and watching the beach from the pier to see if you can spit the sharks before the swimmers...as we did.
My daughters three 10, 7 and 5 got a bit bored with Disney but loved universal. I wouldn't bother taking little ones to Epcot to be honest. It's a huge park and I see it more as a shopping trip. It's ok when they are a bit older, you're staying longer and may want to park hop.
The kids loved Harry potter and each of the two universal parks had a Harry potter area each and my daughter said it was just amazing. No expense had been spared and the attention to detail was just fascinating. I've been to Florida 40 times so we gave the parks a miss last year and I regret it now because I don't know when I'll be back. This OH isn't very keen on Florida lol
My daughter felt disney looked rather tired by comparison. If they've still got that grand ole opry and that big bear thing I'll agree. It was tired when we first went in 1990.
The water parks are good fun but again I would give a miss to do something that is not so easy to get in uk.
I would do
1 day MK
1 day Hollywood studios
1 day Clearwater
2 days universal and islands of adventure
You also need some shopping time. Thankfully the malls are open till late!
Premium or prime outlets are both very good. So is The Loop. I like kohls and you can't beat Ross dress for less for bargains. Lake buena vista outlets have some good bargains. Then there's Florida mall and mall at millennia. I like Macy's best.
If you can fit it in Boggy Creek airboat rides are not to be missed and you must eat at sweet tomatoes, top of I drive or the new one on the 192 and panera bread at the loop and also on the 192 where there is also another Ross's.
Oh heck! You've missed out Downtown Disney as well. You need to check that out. If only to see the Lego store and huge Disney store and if you can throw in a trip to see cirque du soleil you've hit the jackpot!