Add one more vote for Blizzard Beach at that age. Once they get to around 7-8 I would say its a toss up but all 3 of my kids preferred Blizzard Beach at 5
The clinchers for us are the family raft rides & wave pools. My 6-year-old (who is a veteran beach goer) got pummeled 2 or 3 times in TL's wave pool, went to first aid for band aids, and never went back in. At BB, she was in the wave pool for hours.
The family raft ride at BB requires a LOT of stairs or a wait in the chair lift line. But, the line for the ride itself is short, and the ride is great. We honestly lost track of the # of times we rode.
Contrast that with the raft at TL which we had to lug up the hill ourselves. And after a 45 minute wait in line, we experienced the slowest, shortest raft ride ever. One & done.
So, even though BB is considered to have the better "kiddie" area, it's really the rest of the park that wins over the under 48" crowd in my family.
I've only been to typhoon lagoon and the last time I was there was in 2000 so I'm sure a lot has changed. But I remember the floor/bottom of the wave pool to be scratchy (obviously so it's not slippery) but the waves are rough and I remember being knocked down and getting my feet and legs scratched. And I was an adult being knocked over! So you might not like that. But TL has the lazy river which is awesome!