I actually used the Air France Kids Solo service over the summer for my son to be picked up by the grand parents in Paris. With Covid, it was too difficult and very expensive for me to travel back and forth between London and Paris.
It cost €70 for the flight ticket in addition to the €70 euro for the normal ticket I think.
I dropped my son at Heathrow airport and I was asked to wait until the departure of the plane to make sure it was ok. And the family picked him up in Charles de Gaulle airport in Paris. Apparently another kid (6 years old) was also travelling unaccompanied and they sat together. Very good service and when you compare with the price and time and hassle to travel with the child yourself, it's worth the price.

I was just very surprised that British Airways was not offering a similar service . Lufthansa in Germany and Iberia for Spain are doing it, as the article said.