This question is asked a lot, especially as the weather gets warm. Not saying this "snarky" at all, just in a helpful way, try doing a quick search and you'll find tons of threads about it.
In a nutshell, as a family who loves both parks and has been going to them since our kids were babies, our answer is that they're both equally awesome. They have a lot of similarities, and some differences. Key differences:
First and foremost is the wave pool. BB is steady and small waves...kinda like being out on a wavy ocean day. You can sit in inner tubes in it...though honestly it makes me sea sick after a while, because it's constant bobbing up and down. TL is gigantic, huge-like-you've-never-seen-before size waves. But no, it is not unsafe for kids at all if you just use a dash of common sense. We've been bringing our kids in there since they were literally 1 year old. It's a zero entry pool, so just keep your 4 year old in water that's up to his/her ankles or knees and you'll be fine. Strong swimmers can go out into deeper water, and you can "surf" the waves. It's super cool. Just be aware the bottom of the pool surface is very gritty, you don't want to slide on it, you'll get rug burn. It's only a very intense pool if you go into deeper water, by time the waves reach the ankle high water area they're not strong at all. BB has a neat little "Tikes Peak" and "Ski Patrol" area for kids. There's a kiddie zip line, some small child slides and an "iceburg" crossing. It's right up the alley for your 4 year old, but just on the edge for a 10 year old. TL has kid areas too, but doesn't have the zip lines, etc... TL has a new family tube ride that's really cool, giving it two total. BB only has one. TL has Crush N Gusher, a sort of "roller coaster" water slide...it uses jets of water to push you up small hills. It's totally fine for 4 and 9 year olds, as you sit in the same tube, right behind them. It's never "fast", just a new experience. BB does not have this. Really, it's a toss up. If I was FORCED to pick one, I'd pick TL, but literally it's 51% vs 49%, we love them both.
Crowds? Sure, it gets somewhat crowded mid-day, but never anything close to the main park. The biggest challenge is a lack of FP+...at least at the moment. So the "big" slides get longer lines during peak hours. The park will open at 10am in the summer. Show up at 9:55am and you'll spend the first hour going on slide after slide after slide. It's awesome. Same with the end of the night, the crowd clears out fast. Chairs are easy to find, at any time of the day, even in summer.
When they finally expanded it they built in right along a main walkway and each time we go it is chaotic. People are walking through it to get places and it's not convenient at all. I would never leave my kids side there.
