You leave a lot of open ground here so I'll start you off.
Without knowing how tight your budget is we really are at a loss to help you. You may find a great low price on something and then need to spend $1,000 or more for tires to be safe driving the kids around. Are you good at repairing things? Older used campers will develop problems that need some wrenching, plumbing or electrical know how to fix.
Have you ever camped before? If no, you may want to start off with a tent to find out if it is for you and the kids before you drop a bundle of money.
Again with money. You don't list where you are located at. Around the northeast US you can figure on $60 or more a night for full hook-ups for that class C. Tent sites are cheaper.
Good luck! Hope you get the kids into camping.