lift club

Q: A person provides the service of picking up and dropping off school children from home to school. In the morning, he picks them up from home and drops them off at school. In the afternoon, he picks them up from school and drops them off at home. Some days, certain students are absent. For the days, they are absent, will it be permissible for the driver to charge them for it due to the fact that the seat is reserved for them in the car? The contract between the parties is on a monthly basis i.e. he charges them a fee for his services at the end of the month.