I am currently coaching U8's at 5v5. I have never tried to organise the team on matchday into defenders and attackers or anything like that.
All of the teams we've played have had some sort of structure. Ranging from allocating one child as a defender, to trying to play a diamond formation. It seems to be the cause of much stress to opposition coaches because 7 and 8 year old kids want to go after the ball - they do not want to have to show positional discipline.
However, next season at U9 we move to 7v7. Is this a good time to help them be a little more organised on the pitch?