The principal of P.S. 4 in the Bronx called in the report of the gun to police just as school was scheduled to open, the New York Daily News reported.
The building, which also holds a middle school and the Leadership Academy high school, was under lockdown for more than an hour as police conducted a search, the newspaper said. Students were made to crouch under their desks or huddle in corners of classrooms as the sweep occurred.
Police eventually found the children had a Nerf gun that fires foam "bullets," WNYW-TV, New York, reported.
Some parents gathered outside the school during the search, complaining they were kept in the dark about what was going on inside, the News reported.
"When I called, they said nothing was going on," said Vanessa Sanchez, 38, whose first-grade son Adam was inside the school. "It's just incredible that something like this, whether it's real or not, can happen and there's no system to contact parents."
The boy who brought the toy gun to school will not face charges, though he could face discipline from the school, the newspaper reported.