hi there pooh2001!
First off, welcome to the wonderful world of Disney Waterparks!! They are amazing.
Ok, question for you, how old are your kids?
If they are anywhere from age 6 to 13 or 14 I would actually tell you to soend one day at each park and then return for the third day to whichever was your favorite.
You see, both waterparks have kids areas. Typhoon Lagoon has Ketchakiddie Creek and Blizzard Beach has two kids areas, Tike's Peak and Ski Patrol Training Camp.
All 3 of these sections have scaled down attractions that are great for kids.
Also, both parks have family raft rides, where the entire family sits in a big raft and goes down a slide together. Lots of fun!! Blizzard Beach has the longest fastest family raft ride in the world to my knowledge, but its not scary I assure you, just great fun.
As far as wave pools go, if your kids aren't good swimmers then be careful at typhoons wave pool. First off it's HUGE and the waves can reach up to 6 feet! So if you take them there have them stay near the edge.
And whatever don't have them sit at the edge as a wave comes in because the bottom of the pool is very rough and their butts will be scratched (Leaned this from personal experience, ouch! not fun trust me)
Anyways, you will have a great time at both parks. From what I'm aware there are lifejackets for kids at both parks.
Blizzard Beach has a far smaller and far tamer, it is small bobbing waves.
Another great suggestion if your kids cant swim well is to do the lazy river. From what i'm aware, both lazy rivers now offer double tubes so that you can sit in one section and your kid in another but you can stay together and keep an eye on them.
There was a third water park, River Country, but it has been closed for quite a while.
As a person who has visited both parks and loves them both (especially typhoon) you'll have a great time. I'm also a certified lifeguard and can assure you that all the attractions there are safe but use precaution when judging whether or not your kids can handle them based on their swimming ability.
Have a great time! If you have anymore questions please feel free to PM me
