Winkler police said it happened during the Winkler Harvest Festival parade at about 10:45 a.m. CT on Saturday morning.
The young boy was flown to a Winnipeg hospital by STARS air ambulance.
Colin Fast, spokesperson for STARS, said the child was hit after he was handing out candy.
"At some point he walked back toward the route he was associated with to pick up some more candy and something went wrong," Fast said.
Fast said the boy had multiple serious injuries, but he is in stable condition.
Winkler is about 125 kilometres southwest of Winnipeg. The Winkler Harvest Festival will continue until Sunday.