We love Busch gardens! We've had the annual pass for almost 3 years now.
Here's my advice:
Bring bathing suits. Even if you are not sure it's warm enough.
You can bring food and drinks in for the kids. We always bring healthy stuff and snacks along with juice boxes or bottled water for the kids.
Grab a map and schedule at the front gate. "Katonga" is AWESOME for little people. It's about 30 minutes long and the kids will love it. It's also a great place to relax in the AC and nurse when it's hot. I suggest sitting toward the front so that the bubbles and butterflies fall on you.
If your kids like pirates the 3D movie is fun and is also in the AC. Sometimes there are other fun visiting shows. We really like to catch the acrobats when they are there. The birds show is fun too. There are more shows, we just aren't that into them.
There are quite a few kiddy rides. Dragon land is home of the kiddie rides (and more). There are also a few scattered throughout the park. If your 5 year old is 42" there are more ride possibilities. Hight restrictions are on the map.
Adults can "kid swap" on the grown up rides. One adult waits in line and rides. Then the other adult can skip the wait and go up the exit to ride too. This is great if you like to ride roller coasters.
Definitely ride the train. You can see more animals in the zoo part of the park this way. Also, be sure to see the hippos. They are on display in a very neat way. Jungala is the newest section of the park. This area also has some nice animal displays. We like the animal nursery too. You can get a kiss from the baby flamingos there if you are lucky.
My DH says this:
Be prepared to follow the kids around all day and not rush them. (This is what he needs to keep in mind to not be grouchy
Remember that you will not be able to do it all in one day.
Hope that helps.
The website has some great info on it too.