If you go with an N2A card, or better, do it yourself, you'll have access to the Google Play Store (GoPS). That will let you purchase and run a wide selection of apps. Be aware that this doesn't turn your 3 year old tablet into the equivalent of a modern tablet. Depending on the version of Android you boot using the N2A card or have installed, it might run reasonably well.
Many of the launchers, the programs responsible for the user interface you see when you turn on the tablet and which let you drag icons around and uninstall programs, let you lock the home screens. That might suffice for keeping your daughter from breaking things by playing around.
If you don't save your password in the GoPS app, no purchases can be made without a password. If she manages to get into the GoPS app, she might be able to install free apps, or uninstall apps. You can probably hide the GoPS app icon well enough to foil a 3 year old. If not, buy her a state-of-the art tablet and a computer for application development. The kid has a bright future in technology. Encourage her!
If you spend some time configuring your NC, it can be a good platform for running a handful of simple games. Whether it's worth the effort is up to you. It may not run your (or her) favorites.
Personally, I'd learn how to install the Cyanogenmod software onto your NC yourself, since you may have to re-install if she breaks it in the future. N2A and its competitor Android for Nook (AFN) are just repackaging of the Cyanogenmod software onto microSD cards and sold for (IMO) excessive prices. While both contribute a bit of profit back to Cyanogenmod development, N2A didn't initially, and both often promise more than they actually deliver.
With realistic expectations, you can probably do what you want.
thank you for the great advice and post
since my daughter has a sensory disability, she always needs my full attention. I feel that a card would be the best for me.
locking the home screen sounds great if I knew how to do it. as far as the tablet and computer, she has crashed our home comptuer and it still does not run corectly. For now she can use my Nook Color untill we buy (Nauby?) for her
sounds like a great little tab for kids
on a side note, which card would be better
N2A or the A4N ?
thank you again and keep up the great support for all of the tablet users