If you let your children use your iPad I would suggest that you turn off the ability to make in-app purchases. Otherwise a free game that your child is playing could end up costing a fair bit of money.
To do this you need to enable parental controls by going into settings and general. Within parental controls locate restrictions, enable it and enter a passcode. Once enabled scroll down the until you see In-App Purchases. Turn this off and then most apps won’t even show the screen for purchasing items or will not be allowed to make purchases.