The victim was hit several times outside a Sainsbury’s superstore on the outskirts of the Co Down town.
Police said it was lucky the youngster was not killed or seriously injured as well.
The shooting is believed to have occurred at about 3pm on Sunday in the packed car park, just off the Balloo Link road.
Detectives say there may have been more than 100 people who witnessed the shooting.
Superintendent Brian Kee, district commander Ards and North Down District, said: “Our thoughts are very much with the family of the 35-year-old victim at this extremely difficult time and I condemn this brutal, senseless and horrendous killing.
“This cold blooded murder was carried out in broad daylight in front of families who were out enjoying this Bank Holiday weekend.