If you were to take SQ or CX, they are pretty reliable.
But the best is travel during non-peak period cos if the flight is full, the stewardess are usually very stressed and tired and may not be able to take care of your child.
But CX and SQ policies for handling of young person travelling alone is pretty good. Accompany for boarding and handover.
Do seat your son near the work galley which is easy for the stewardess to take care of him.
Hopefully your son is not shy? Cos if he ask, he usually gets what he wants.
:)hope this helps.
Dont be worry, my son just travelled to new zeland last year when he was 8. 唔洗緊張, 全程如果做了UM (好似 $800), 個空姐會take care 的, 只要在check 完out, 佢會將要做UM的group在一起, 連passport 同填表都同你做的, last year 我要求俾阿仔自己都唔得, 不用擔心