To investigate further, you can see a history of when time limits were changed by opening TimesUpKidz, clicking Security Tips, and following the link at the top of the page.
If limits got changed and you didn't do it, the most likely and common explanation (which you don't want to hear!) is that your child guessed your password or walked up to the computer while you were logged on and started the TimesUpKidz program. Make sure your password is tough-to-guess, and don't forget to choose Log Off or Lock or Switch User each time you are done using the computer. Pressing
WindowsKey + L is a quick way to do that. Another possible explanation is that your child has an Administrator account; read more about types of Windows user accounts