How do you all transition in new children, particularly 12month olds?

I have my 5th child joining soon, another 12month old. The parents wanted to come and spend 2-3 hrs here for a few days with their child.

I told them that wouldn't work that I would have them out for an hour over the weekend and they can come 15min before I open and leave after 30min before my 2nd child arrives. I have a little boy who is easy going and awesome but can not handle random adults in the daycare. When my last girl started he was perfectly fine except during the girls drop-off and pick-ups he would SCREAM until the other kids mom left...twice a day, every day for just over a week. Then bam, perfectly fine and now waves to the mom and smiles. That mom was great about it and she was in and out very quickly and dressed her child upstairs out of the daycare so the boy would calm faster. We communicated through emails since I couldn't even discuss her child's days as the screamer was just so, well, screamy!!

I explained this to the new family and explained that having their child start off with another child screaming and clinging to me helps no one. The other child that started was the easiest kid ever and didn't care at all.

They said they will follow my lead on this but that they are surprised they can't come and stay for the first few days.

Is it common to have parents stay in the program at first? Do the other children accept this? What do you do when parents are sitting there in the room for hours?

The family doesn't seem to mind, they understand as I explained why. But I would like to know what others do should a family in the future make this request again!