For that age, I would go with Blizzard Beach.
I think the little kid area is better.
The bigger kid area has a raft slide the little ones should love.
The wave pool will be fun for them and not terrifying for parents of 4 year olds like the one at Typhoon Lagoon is
The family raft ride is much longer and much better
They can even do the head first mat slides (my kids loved them at that age):
Snow Stormers - Just make sure an adult goes first to catch them in the deep pool at the end.
Toboggan Racers - There is no pool at the end, just an inch of water. Plus 8 people go side by side at the same time. The slide operators at the top will help your little ones get going if you ask them.