Hi,
I suggest that you post this in the "Which One Should I Buy?" forum. This one is Introduce Yourself.
It's a good idea also to mention your budget , where you bought these comics from/what format they're in, and where you're planning to get them in the future (Comixology? Library? Somewhere else?)
The parental controls issue might be on the tricky side with some tablet devices, but I know
iPads have them to a certain degree. However preteens are pretty smart; there's a good chance they'll figure out how to circumvent any technical controls you place, if they are motivated to do so. So human supervision is needed if you have concerns, as with all network-enabled technology.