Most important thing: Get a hard case for it ASAP!
It depends on which version, as some have limits to what you can do. I only have experience with the B&W and the Color(I think) versions.
Is it a NOOK Color? Goto the B&N Website and d/l the manual(if you haven't already), and also check out the free kids books--they have tons for kids, and interactive books for the Color tablet. Goto NOOK for kids, and select price range at $0 to find the freebies.
You also want Kid's Place:
http://www.barnesandnoble.com/w/kids-place-parental-contr...
It's a Parental control for NOOK, like the Kindle's Free time, but not quite as flexible, yet still a must to protect you and your munchkins from the occasional accidental purchase.