The Firefighters (1975)

Bob, along with his brother and sister, lives next to a fire station. They call themselves the 'Bramley Junior Fire Brigade' and follow the engines whenever they can. When Bob reports a fire he is commended by the brigade but suspicion soon falls on him when the fire is found to be the work of arsonists. It's up to the Junior Brigade to find out just who is responsible, catch them and clear Bob's name.