If they are good at what they do, they will ignore you, or perhaps ask you to leave the field. Either situation is at best distracting and at worst reflects poorly on the team's overall sportsmanship. Publicly criticizing players on your team can really hurt team morale. They will not need reminders from their families, friends and other spectators. The players for the other team are also trying hard and in truth are probably no meaner or nastier than players from your team.
Criticism is simply poor sportsmanship and leads to unnecessary bad feelings on and off the field.
The unfortunate spectacle of a supposed adult shouting insults at a child on a soccer field is merely disgusting. Soccer is a game, not a war. Don't coach players from the touchlines, or for that matter while THEY are on the touchlines. In most leagues, coaching from the sidelines is frowned on, and rightly so. Soccer is different from most sports in the US, because it is a game of the players.