What should I do if my child's passport is about to expire while we are in Thailand and he may overstay his visa?

Overstay for children advice:

We’ve run into a bit of logistical situation regarding our 4yo passport- his passport just passed the 6 month validity mark (meaning still valid, but only 5.5 months left) and we were planning on leaving this week, however we were just notified that although the country we are going to only requires 3 months of validity, the airline requires 6 months and can refuse boarding. So we are left with 2 options- apply for emergency passport or apply for a new passport but my son will then be overstaying his time in Thailand. My husband still has 3 weeks left on his 30 day extension, and myself and the youngest could technically do a visa run, so it would only be the 4year old that is “overstaying”. The processing time at the US embassy is roughly 3 weeks so we can assume he’ll be around 3 weeks overstaying, give or take a week or so. Has anyone had experience with this? Will we be charged the 500baht/day for his overstaying or is that only charged to adults?

Thank you for the help!