Hello and welcome to Apple Support Communities, faye238!
I understand that you've setup Screen Time on your son's device, however, they are able to bypass the blocks by ignoring the alert. I'd be happy to provide information to help you setup Screen Time correctly.
Use the following steps on your son's device: Use parental controls on your child's iPhone, iPad, and iPod touch
"Set Content & Privacy Restrictions
- Go to Settings and tap Screen Time.
- Tap Continue, then choose "This is My [Device]" or "This is My Child's [Device]."
- If you're the parent or guardian of your device and want to prevent another family member from changing your settings, tap Use Screen Time Passcode to create a passcode. Then re-enter the passcode to confirm.
- If you're setting up Screen Time on your child's device, follow the prompts until you get to Parent Passcode and enter a passcode. Re-enter the passcode to confirm.
3.Tap Content & Privacy Restrictions. If asked, enter your passcode, then turn on Content & Privacy."
It's possible that when Screen Time was setup, the option of "The is My [Device]", was selected. He would therefore be given the option to ignore any time limits set.
I hope this helps!
Enjoy your day!