CHICAGO (CBS) — An elementary school on the North Side has warned parents to keep a close eye on their kids, after a man tried to snatch a boy from the school playground.

CBS 2’s Susanna Song reports a man tried to abduct a 4th grader from the playground at Alexander Graham Bell Elementary School at 3730 N Oakley Ave on Wednesday, according to a letter sent out by the school.

Police said the man approached the boy and told him the boy’s mother had sent him there to pick him up from school, because she was sleeping.

The boy ran away and found his mother, and the man left the scene.

Police have not released a sketch of the suspect, and had only a vague description of the man. He was wearing a stained black shirt, flip-flops, and a blue Cubs hat.

The letter from Bell warned other area schools to be on the lookout, and urged anyone with information about the kidnapping attempt to call police.