Yep, splitting the family can cause hiccups. Took lads BKK-LHR in 2007 on THAI - me in First (rearmost seat), 2 lads (13 & 15) in Biz in the front row - so just the door between us. They weren’t technically unaccompanied minors, but I did need to chat with the ISM when it became apparent to the Biz cabin manager I was in a separate cabin - albeit only 3m away.