I'd skip it! We have 3, and we have never done the water parks yet.
1st trip - DD 18 months (too young)
2nd trip - DD 2 1/2 and DD 8 months (too young)
3rd trip - DD 4, DD, 2, and DS 10 months (too young and how do *2* parents keep *3* kids really afe at a water park when 1 of them isn't even walking and none of them swim?)
4th trip - DD 6, DD 4, DS 2 1/2 (still too young, too un-self sufficient to be safe at a water park, still don't like the aduclt to child ratio for a water park)
In your case, I would say the *8 month old AND crazy toddler* would be quite a handful at a water park!! I have no trouble keeping my kids safe at an amusement park, but water adds a whole new level.
If your 5 year old would just love it -- and your DH -- can you split up for the afternoon. Maybe you could take the 2 smaller ones to something they would enjoy - a character meal or something a little calmer and a little safer. Just a thought.
Maybe Blizzard Beach would work - I haven't been - but sounds like you would hav eto split up anyhow.
Good luck on whatever you decide. I can't wait until alll 3 of mine are swimmers....then we'll hit a water park together! They sound great.