We usually do two days at Sea World. It's our favorite of the great Orlando theme parks. I think you and your five year old will most likely love it!
Some people because of attractive pricing deals will do a combo Sea World, Busch Gardens, and Aquatica (attractive pricing because of the same company owning all three) and make it a week doing Sea World twice, Aquatica twice, Busch Gardens usually just once as it's a long day because of going all the way to Tampa and back -- there is a shuttle if you don't want to drive it, and filling in the other day or two in a week long vacation with a resort day / shopping day.
There are combo ticket with Discovery Cove too that are quite a bit pricier. There is also a flex pass for those who want to combine Sea World / Aquatica with Universal Parks (2 of them) and Wet and Wild.
We ourselves, usually just pick our own stuff on a trip: Last week long trip was at an offsite condo and for our six days, we did Sea World our first and last day, did Aquatica one day (combo ticket with Sea World had good pricing), had two resort down days -- on one of those we saw the Titanic attraction and on the other we visited Disney Monerail resorts, and did a Disney Park one day,
March 2011 -- We have six days again and will do Sea World our first and last day, two resort down days (tennis and swimming), one Water Park Day -- doing Disney's Typhoon Lagoon, and one day at Universal's Islands of Adventure to see the new Harry Potter stuff (We'd normally do a Disney Park day rather than that as we prefer Disney to Universal, but are curious to see Harry Potter theming so will switch that this vacation only).