The likes of messi, xavi, iniesta, robinho, robaldinho, ronaldo, kaka, and most other south American footballers have been brought up on small sided games.
Trevor Brooking has been pushing this for years.
Apart from their debuts, not many of your list were regulars at that age, mostly just the odd game.
If you have a ten year old kid, only four foot tall and put him in goal on a full size, how does that make sense?