I have a blanket 'no' rule for any apps that actually cost money.
I went down this road because the ipad was a present to me from my DH and I didn't want it to become yet another thing I get hassled about. Because of this blanket rule my DSs (11 & 6) don't ask for apps that cost money and just play on the free to download games.
But most of them are really short lived and they get bored with them quickly.
Are there any apps you'd recommend for these ages, that I could buy them for a small Christmas present?