do you take your toddler/preschooler to waterparks?

Water parks, no. The ones around here are all really big and crowded so we're waiting until the kids are older. We do go to the pool every week.

There is one amusement park we go to and we buy both kids season passes. It's a smaller park on the beach (so not a large six flags type) and there are lots of little kid rides, my 2.5 year old dd can go on 10 rides. Once my ds outgrew his fear of rides, he was about 3.5, we started buying him a pass and so far dd is not scared of rides so we buy her a pass too. We do not buy passes for dh and I, there is no admission and you just pay for rides. With the two kids, we never get the chance to go on the big roller coasters and such, so we just buy a few tickets for us to go on the ferris wheel, carousel, cave train, etc, as a family.

Yes, we started oldest dd at 2yrs old for the amusement park.  They both love rides and water parks. 

We've been going since my son was two years old.  But we also go to a smaller place.  It isn't as crowded and doesn't have all the big water rides.  It has a really large pool, two splash areas with some slides, a lazy river and a wave pool.  There are also three large slide, but we don't do those.  They also have a ride side that is included, but they remind me more of fair rides than big amusement park rides.
 

It depends on your kid. M is 5 and doesn't like water parks, but baby boy loves them.

However, we bought annual passes to Disneyland when M was just 2 months old because she LOVED it.

Water parks, yes, we bring them and they both love it.

Amusement parks? Not large ones. Admission is sooo expensive and they aren't big enough to ride anything other than the kiddy rides. We can do the smaller family parks for 1/4 of the price, a fraction of the crowds, and the same rides (for them anyway, the adults are SOL haha)

We have been taking Ds to the water park for three years now. We have to buy him a season pass, and there is not discount for a kid's pass. :( He got once or twice a week. They have a huge kids section which this year he does not have to wear a life vest in. He can do everything by himself. He has been going one of the big slides for the past two years. Last year he would ride down with Dh or me, but the end of last year he would ride down after us so we could catch him at the bottom. This year if it is not crowded I let him go to the top by himself, since I can see him the whole way up, and wait in the pool at the bottom for him. He has to wear a life vest in the adult section and the life guards strictly enforce it, not that they have had to with us. He loves the wave pool and this year he feels he does not have to hold my hand, so I make him stay in the shallow end. Last year he started going down one of the really big slides with Dh, they have special innertubes that have a bottom in them, so he cannot fall threw. Dh sends him down first then he follows. The life guard at the bottom pulls him to steps and he holds on to the rail till Dh gets there. If I am at the park with them then I help him out. We all have a great time!!

Amusement parks are a different story. All the ones around here are really big and mostly adult rides. We are going to take him this year, but I have a bad feeling Ds and I will spend all day riding the train around the park. Last time we went, two years ago, he cried on everything. We went to the state fair last year and he loved all the rides, so we will probably take him to the carnival when it comes this way. The rides are much more kid friendly.
 

A town about 20 miles away from us has a large swimming pool that has tons of toddler-friendly things.  It's free for DD to go, so I bought a seaon adult pass for myself to take her.  The nearest amusement park or water park is about 3 hours away, so if we would go, we would just do a day pass.