If you feel a child is not doing what should be done, tell the coaches, not the player. Either way, a parent can help a player's athletic development much better working together with the coaches, not independently. Do not crowd the touchlines for any reason and stay away from the goal area to avoid interfering with those involved in the game. Don't forget, YOUR attitude on the touchlines can affect the mood and success of the team. If the coaches think that your touchlines activity is hurting team performance in any way, they should promptly advise you, hopefully without ruffling any of your feathers.
Emotions run high during games, and feelings are easily hurt.
Nevertheless, any spectator, whether parent, friend or player, who persists in inappropriate touchlines behavior after being warned by the coaches should be asked to leave the vicinity of the field. Coaches should not argue with parents at the game. If YOU want to talk about the game, call the coaches later at home or get them aside after the game. I'm tired of saying the same old stuff about parents and their role as spectators on the soccer field, but since it remains an ever-increasing problem, I will continue to beat this dead horse until I pass out from exhaustion. I would rather have to watch cats in the backyard through the sliding glass door, than to sit next to one of these soccer parents.