Capacity is measured in coaches. A hundred children arriving at ten means every activity, every toilet and every covered space is occupied simultaneously, so two schools on one morning has to be a deliberate decision rather than an accident.
The animals set a limit nobody else does. Handling sessions have to be rotated and rested, and a farm that books beyond that is trading the welfare of the animals for a morning's revenue.
Forms must arrive before the visit. Allergies, consents and medical notes for a hundred children are useless on the day if they are still in a folder at the school, so chasing them is part of the booking.
School payment is its own process. Purchase orders, invoicing to a bursar and payment weeks after the visit is normal here, and a farm expecting payment on the day will spend its time chasing instead of teaching.