Birthday party?

I'm throwing a birthday party for my quadruplets a little early this year. They will be turning 3. I'm doing it early for two reasons, one I want to do it before my daughter has her baby and two because it will be a pool party and I need to do it before it gets cold. Does this sound like a good party idea? We will have it in the backyard, we have a screened in pool with a hot-tub for the older kids who can swim. Along with a slide. But for the little ones out in the yard we will have a bunch of those little blow up pools. Can anyone show me some of those things, that aren't extremely expensive. We are also going to rent a big water slide for the older kids. This party is also for 3 of my older kids. (Gabriella will turn 8, the twins will turn 7, and the quads will turn 3) But if you can show me some of those slides that would be awesome. I'm going to put out some sprinklers also, but there will be little kids there. (16-18 months) who can get in the little pools with their parent