Can worlds from the minecraft beta program be taken off of the beta program and played on...

Your son is playing on the official release channel for Minecraft. His 1.12 version is currently the latest official version, whereas his friends have joined the Insider Program and are playing a beta test version of Minecraft.

His friends can either un-enroll from the Beta Insider Program, or you son can try to join the Insider Program and update his Minecraft to a beta version.

Be aware however, that beta version still contain untested parts, and the game can crash, malfunction and in turn destroy worlds if an error occurs.

If your son is still willing to test the Beta, he can download the free Insider app from the store, and join the Minecraft Beta.

Then he'll have to download/update his Minecraft to the newer beta version.

When you delist the game from its beta client back to the current version that is publicly avaliable, you will lose access to any world that was in the beta version until the update that was in the beta version comes out to the regular base game.

It is very confusing I know. To make a long explanation short, you can go back to the game outside of beta but the worlds saved or created in the beta will be locked until the game gets an official update. You'd get an "outdated" error or something similar
to that. Unless you are trying to play with someone who doesn't want to mess with the beta it isn't really advised to leave it because you may have to temporarily start a new world.

Hello Dracos,

Thank you for posting here on the Xbox forums. For in game questions, especially involving betas, it would be best to get in touch with the developers support.

You can find
Mojang support here, and the
Minecraft forums here.

I wish thy would make it so I could do that.

Unfortantly they can not be moved to the non beta version