Which waterpark?

[Tinkerbell]

With kids that age I’d go for aquatics.

We went with my niece the year it opened she was 5 loved it. I can also recommend hiring the cabanas, we did and it was a godsend. Had my mother with us as well it gave good shade and a quiet place to be away from the humdrum

I’d like to go this year but with 14 days onsite at Disney it’s too expensive for us for one day... I think... ooh. I don’t think I’ve checked

[Mumtotwo]

Have to say we love Aquatica

[Lisbon]

Haven't been to Aquatica but out of the others we prefer blizzard Beach - seems more open and clean and plenty of different rides - remember going around lazy river with my son when he was about three and him falling asleep on me - happy memories
Rob

[cornishfrogboy]

Another vote for Aquatica. With the age of your children, the child's play area ticks all the boxes.

My personal favourite is like many others, Typhoon Lagoon. The only snag for younger visitors is that the waves in the wave pool can get rather big and knock youngsters off their feet. The. Bottom is rather rough and causes grazes.

[GetMeOnHoliday]

My favourite out of that list would be VB, although I'm not too sure how appropriate/interesting that'd be for the grandparents and 4yo given I feel like that's more intense with more bigger rides than other parks

Given what you've said I'd say Typhoon Lagoon which would be fun for all