Oh, we really like Alton Towers!
Haven't taken out youngest 2 up there during Scarefest (purely time/ money reasons), but took DSC twice quite a few years ago- I think they were 6/8/10 at the time and they loved all the daytime Halloween stuff.
We were lucky enough to stay at SplashLandings for 3 nights this summer- youngest member of holiday was DD2 (2), and there was plenty to keep her entertained.
Like a pp mentioned, definetely get the parent queue pass from customer services as you enter- we've always used it that one parent queues with 3 or 4 DC, gets pass stamped at end of ride, then second parent enters ride with remaining 1 or 2 DC down the fast track or disabled entrance to ride almost immediately.
Food-wise, we had hot buffet breakfast included each morning- nice food & plenty of variety for everyone.
We packed a huge box of pre-packed picnic food (fruit/ crisps/ cakebars/ pepperamis don't need refrigeration etc), for our lunchtime meals, thinking we wouldn't be able to keep stuff cold.
On arrival at Alton Towers we requested a mini-fridge for our room (originally just for milk for DD2/ our coffees etc), which was actually large enough to store loads, so we bought some cheese/ ham/ bread etc for sandwiches. There is a small convenience shop in the Enchanted Village which sells all-sorts like that, and isn't too expensive. Or if you want more variety/ cheaper, then there are a few co-op type shops in the little village 5mins drive out of the front gate of Alton Towers. The reception staff had the fridge brought to our room within 20mins of arrival- it wasn't treated as an odd request, so I'm sure you could get one brought to your Enchanted Village room.
For evening meals, we ate once in Crooked Spoon in Enchanted Village which was lovely- £15 for a main/ £7 for a child's dinner/ DD2 ate for free off of our plates- they provided her with plastic tableware. We didn't have starters or puds to keep costs down- had pre-bought sweets & cakes for afters later at the evening disco.
Also ate once in Flambo Jambos "all you can eat"- think it was £16 for adult/ £8 for child/ DD2 free again, for unlimited pizza/ pasta/ puds etc.
Also had a Chinese takeaway delivered from the local village- huge portion sizes etc. They delivered to reception and called our room to let us know they were there. Reception told us to collect plates/ cutlery etc from Flambo Jambos, and to leave the used dishes next to the tea/ coffee making facilities in our room for housekeeping to clear it away the following morning. I'm sure you could get your plates/ cutlery from Crooked Spoon as that's your nearest, and it's so much nicer not eating with disposable stuff.
In the park, you can buy a £5 refillable bottle, which you can have filled at any snack station for free- Oasis/ fruit juice/ water/ fizzy, which cut costs for us on buying seperate drinks or lugging our own drinks round with us.
Entertainment in the evening is great- you have free access to both Alton Hotel & Slash Landings hotel- both have great kids discos and entertainers from around 5pm til midnight. We took our own kids' drinks & snacks to the evening shows to keep costs down on using the bar etc.
Hope you have a great stay! :)