no. They used to collect photos of all the kids and put them on some school form. Only the teachers had to go through immigration whilst the kids stayed on the bus. i don't think the system has changed since i was at school
I'll ask my wife tonight (she's a teacher) excatly what the technicals are but basically the children don't need passports, they are declared as a group by the teachers.
my daughter is just back from a France trip. We had to fill in a form and send in a passport photo, from what i can remember it was to form part of a group application. She certainly didn't need to take her own passport.
It must depend on the school then. Last time I went, we did all have to take our passports and each one was individually checked by a Customs Officer in a car park on the coach.