What Gant says. In the league my daughter plays in, any goal differential over 4 leads to a player pulled from the field, which levels out the game relatively quickly but keeps the skill development alive. There is nothing more frustrating to an overmatched team than having the opponent start to play keep away. Does nothing for skill development, and is frankly worse from a "self esteem" perspective.
I personally think full side games are sort of pointless at this age. I'd rather see lots of short 4v4 or 6v6 games. It's really the parents who like to see the full side games. For the kids, it descends into mob play around the ball really quickly.