Traveling with my wife and son on BA207 LHR>MIA and choosing seats.

29K seems a good option as 28K in front doesn't exit and can utilise the extra legroom, but not sure if it's classed as an exit ROW or just the one J seat?

My son is 9 so is he going to be allowed to be seated in 29H or J, even though they seem to be normal seats and only 29K is an exit seat?

Online checkin seems to let me - with only warning coming when choosing 29K - which will be one of us adults.

Any advice?

Thanks

Steve