Skill wise you can separate kids..but at 6 to 8 there is not going to be alot of separating..so we end up separating by size..strength and speed..
When my son started at U10 some eight years ago there was one boy the three teams in the age group fought over to be on their team..He was what I would call a man child..Bigger and faster then everyone else..Two years later his skill was no better and he quit..My son and this child were good friends so I would talk often to the young man and asked him why he quit..He felt like he was not good at it anymore and was not the star on the team..What happened? The players finally caught up to his size and strength..
Let's also not forget the kid that has very little skill and can not for the life of him juggle a ball but plays the sport with great emotion and has the will to win..
We would of separated him at six years old?