Is there a minimum age requirement for doing a border bounce in Thailand?

unless you're bouncing the children out to get them off an overstay and onto a visa exempt so they can get an in country visa issued there's little advantage or reason to bounce children out and back.

Children under 15 cannot be fined for overstay and children under 18 cannot be banned for it. <- now that's not saying they don't need a visa, it's saying there are no penalties for them overstaying. I know foreign kids here who have been on multi-year overstays, exited/re-entered without any issue and then overstayed longer 😮

Just wanted to give you that option.

Richard White Nongkhai and Muhdahan Lao are fine to go in and out of as is the Chiang Khong crossing with Lao up in Chiang Rai

For Cambodia Ban Laem and Ban Pakard don't require overnight stay

Poipet Cambodia required a night stay, Myanmar closed. So choose a hastle free point.

As long as the child has a valid passport AND you pick a border you can get out of and back in to thailand the same day there's no age limit at all. Remember some border crossings want you to spend a night in the other country before you come back in to thailand so check that before you slog to the border to bounce out and back