If you want to make a kids app... Forcing the child to do a number of math problems to continue using the tablet would be an amazing app that I would definitely pay for.
My daughter is a second grader. If every 5 minutes of tablet use 'cost' her 5 correct arithmetic answers she would be working at space x right now.
My daughter is a second grader. If every 5 minutes of tablet use 'cost' her 5 correct arithmetic answers she would be working at space x right now.