As @Matthew says, fouls at younger ages are often due to clumsiness or not yet being that good at football (no disrespect to the youngsters) as they've not been playing the game long. I've very rarely seen a player that's gone in for a tackle that age and looking like he's meaning to hurt the opponent or with, as we hear a lot, no intention to play the ball. I'm not saying that if a caution at younger ages is warranted I wouldn't give it, but I'm certainly a touch more lenient when it come to younger players.
