|To disable Internet Explorer:|
Start>Control Panel>Programs & Features>Turn Windows Features On and Off, then uncheck IE8.
Set up a limited user account, a second account for your access, and an administrator account. The Admin account has full access to all features and needs a strong password that cannot be guessed. Your User account will need normally full access granted by W7 and a good password so you can install new programs, uninstall programs, and do general maintenance. The limited user account needs an easy password (pet's name, etc), but will not have rights to install programs, change windows features, and can only access files saved while under that user.
I still think you are probably going about this wrong though. All children will need to be internet and computer savvy to do well in this world when they grow up, and it is best to teach them the proper way, is when they are young enough to still be willing to listen to us.
You have to be a little bit crazy to keep you from going insane.
If all else fails, read instructions.