The England international, who has been out of action for the Red Devils due to injury, was on his way to watch the former Premier League champions take on Tottenham Hotspur at Old Trafford on Saturday when he stopped to help the boy and his distressed dad.
Michael Robinson, who saw the incident, told The Sun: "We were on our way to the game when we heard a sickening thud. When we turned round we could see this young lad on the floor screaming and shouting.
"As we got closer I saw that Ashley Young had stopped to help the boy. There was blood on the back of the lad's head and he was crying as his dad held him in his arms. Ashley was on his phone and seemed to be very concerned.
"The lad seemed more shook up than anything but then he seemed to get worse. Ashley wasn't bothered about kick-off. He waited with the young lad and his dad."
Once medics arrived at the scene Young left to watch his side lose 3-2 to Tottenham Hotspur.