I second the vote for Beach Club.
I just got back yesterday from a trip with my husband and daughter (who turned 5 during our trip). The Stormalong Bay pool is perfect for this age group!!! There are shallower sections for younger kids, deeper sections for kids who are ready to handle it, a part where you can build sandcastles, a lazy river with tubes, and best of all, a shipwreck with both a short and just fast enough slide (~18 feet?) and a longer extremely fast slide for the daredevils. Since my child is a rather outgoing only child, we wound up striking up conversations with a fair number of kids. I would ask them "What has been your favorite thing about Disney so far?" Several said "The pool." It really is that great.
I think cramming in SeaWorld and/or Universal might be a lot in 6-7 days. Here's what we did on our first 3 days, just to give you an idea. I should mention that we don't like to rush around too much, and also that my kid is much more into the characters than rides.
Day 1--Flight arrived at 10:30ish. A
12--At hotel aafter grocery stop to get water, soda, fruit, sunscreen, etc. Checked in early, had lunch.
2--POOL!
6:15--Dinner at Garden Grove at Swan with Rafiki and Timon. (Food was nothing special, but we do like The Lion King.)
7:30--Made smores on the beach.
Day 2--Epcot Day.
8:35 AM--Breakfast with Princesses at Restaurant Akershus. Met Belle, Aurora, Snow White, Jasmine, and Mulan.
Also got lucky and met Mary Poppins outside.
9:20 or 9:30--Hit The Living Seas pavillion. Prioritized this as apparently lines get long later, and we like Nemo. Did Nemo ride, then Turtle Talk with Crush (very funny). Then toured the aquarium, which my child really loved.
11ish--Browsed gift shop.
11:15--Headed off to Food and Wine Festival. Stopped to see street performers in the U.K., which my daughter liked. Then got unadventurous eater her chicken nuggets at the McDonalds stand. Then husband sampled some sushi. Then we both got some kefta from Morrocco. Got daughter a Mickey ice cream bar. Daughter was not that excited by the country part of Epcot, which was also somewhat crowded due to Food and Wine Festival. On a previous trip, she had really enjoyed the Chinese gymnasts, but they don't start until later. She was more interested in heading back to the hotel.
12:30ish--Headed back to hotel.
Brief rest. Pool time.
5:30--Dinner at 1900 Park with Cinderella, Prince Charming, Anastasia, Drizella, and Lady Tremaine. Very fun!!!!
Day 3--Magic Kingdom Day
Arrive around 7:30 or 7:40 (Little Ones Early Magic Hour Day).
8-8:45--Played games with Peter Pan and Wendy. SOOOOO FUN!!!!! Highlight of trip.
8:45--Rode Many Adventures of Winnie the Pooh ride.
9--Played on Pooh playground.
9:30--Rode Buzz Lightyear.
10-10:40--Met Ariel in Grotto, after lots of fun getting drenched in fountain.
10:45--Rode Peter Pan.
11--Rode It's a Small World.
11:20--Were heading toward Adventureland, when dd announced she would rather play in the Pooh playground some more.
12:15--Checked in for lunch at Cinderella's Royal Table.
1:15--Browsed at Tinkerbelle's Treasures gift shop. Actually bought something: a charm bracelet dd made.
1:50--Back to hotel. NAP.
5--Dinner at Crystal Palace. Met Pooh, Piglet, Eeyore, Tigger. I loved this buffet.
7-10:30--Mickey's Not So Scary Halloween Party!!! The other huge highlight of the trip. Great Villains show, great parade, great fireworks!!!! Got to meet Cruella de Vil, Mean Queen, Maleficent, Jafar, Captain Hook. Super fun.
So that's probably more than you needed to know about us, but it just gives you an idea of how much there is to do...and we only did a small, small sample of the things available.