Multiple drop offs in one day

I'd like some advice on how I could change the wording of my contract so that parents understand how disruptive it is to pickup kids for an appointment and then drop them back off in the last hour or 1.5 hrs of the day.
I have one parent who seems to do this frequently in the summer. I'm not talking about a mid day appointment, but a later one, and then dropping off again. The infants/toddlers don't fully understand the concept of time, but they do understand that after p.m. snack, mom or dad will pick up, and then this one parent will drop off for the second time. Often I get crying/behaviours from the youngest other children in my care when this occurs, and it takes a while to get them all calm again.
I might add, this parent is in a job where they get summers off, so it is not a work issue of needing to get back to the office.
How do I tactfully word this to the parent, and what wording do any of you use in the contract to avoid this scenario.
I'd almost consider this to be drop in care, for which I charge a higher daily rate. Is there a way to deter this behaviour?
Any advice is appreciated! Thanks!

Hi, I think you should just tell them on how their child took a long time to settle down. Also ask them if their appointments can be done early during the morning and bring back right before lunch. Suggest to them that maybe that would help the child settling down easily. I have not written in my contract.

@peacefulbird-it is not the child being dropped off that is having trouble reintegrating in the group, it is the other infants/toddlers that get all upset. Presumably, they can't process why mommies and daddies keep coming and going all day, and triggers them to miss their own parents/expect that their own parent will arrive soon.

"Coming and going from daycare several times in one day is very disruptive to both the routine of the child but also the day home program. It is expected that children are dropped off and picked up only once each day. If a child has an appointment during daycare hours, then please let me know in advance which half of the day the will be present."

I suggest to parents to make the appointments either early in the morning or after nap as it is hard for the child to say bye to the parents twice in one day as this is soo true