BA are great
my 6 year olds twins did Manchester-New York nonstop with BA several times between 6-10 year's of age, and my 10 year old son did it recently, and all were fine. I would almost say they prefer not having us parents along! They are still very proud of how independent they were at such a young age! My son got upgraded to Business Class on the way out. They probably sussed he sleeps a lot when travelling, so realised there was no risk of aggro in the business cabin.
I'd never consider this though with delicate/highly string kids, or where they had to make connections etc.
G