Hatton's good but might be a bit young for them. It's been a long time since I went, though so worth a look at the site, or asking others who've been recently.
You can rent boats, kayaks etc. from either St Nicholas Park in Warwick or next to Jephson Gardens in Leam. St Nicks has a mini fair ground as well and its a decent spot.
Mad Museum in Stratford is decent and it's in the middle of the town centre so you can mooch along the river after. Loads of Shakepeare shite as well if that's their thing!
If they like swimming, the Wave in Cov is good but not cheap and the queues for slides can be a bit sh*t. Newbold Comyn has a decent pool and there's a pub opposite with a playground.
DM me if you've got any Qs about any of that. My two are 11 and 9 for reference. Hope none of it is needed and the game's on, mind!