Would you give me your top tips re: iPad for kids?

Grandparents are giving our 7 and 9 year old daughters iPad Minis for Christmas. (I don't know whether to smile or cry... We get to manage them.)

1) I have an iPad 2 with lots of kids apps already installed, which they enjoy. I would hate to re purchase these. However, I have many apps that aren't applicable to them. I don't want my stuff, emails or messages ending up on their iPads, obviously. Do you recommend setting them up on my AppleID with their own iTunes profiles, or setting them up on their own iTunes accounts without a credit card? Either way, I will be controlling purchases, restricting app purchases through the controls.

2) Can I set up their own iCloud emails accounts so they can message with us, but sync on my AppleID?

3) Do you know of any time limit apps?

Any other childproofing tips? (I'm aware of the security settings, and relatively adept at iOS7.)