Recess: School’s Out (2001)

When the summer comes and all of his friends head to summer camps, T.J. feels a bit left out. He starts going round the city on his own and doing things on his own, but bored by his loneliness, he eventually joins Randall.
When walking by the school, T.J. sees something estrange going on at the backyard and he tries to tell both his parents and the police. Neither of them believe him and he ends up blackmailing his sister so they can go and pick up his friends from their summer camps, who finally believe that something is going wrong and decide to make a change