imessage app not working

After updating my son's phone, his imessage app will not work. When launched, a white screen will show for a few seconds before crashing the app. I tried restarting and force shut-downs but nothing worked. I had this issue before, and fixed it by signing out and back into my iphone, but my son's parental restrictions don't allow him to sign out. I tried changing them but they won't sync, and when I attempt to change them on his phone after clicking the screen time image in settings the app freezes and then crashes. Thank you for your help.