How do I get into my iPhone when my son changed his passcode and forgot it?

If your iPhone has iOS 15.2 or later installed, check out this link→How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support. Otherwise:

See this Apple support link→If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

Or watch this companion video ⬇️

After restoring the phone using one of the methods above you can restore your most recent backup.

The support article you came here from should provide you with one method to try to resolve this issue. Have you tried them all yet? If so, and if they didn't help, I suggest trying this support article:

• If you forgot your iPhone passcode - Apple Support

If that still didn't work, then you should contact Apple Support directly. To do so, simply select the "Get Support" link in the upper right-hand side of this forum's web page.