My handbook states that once the parents arrive, THEY are in charge. But they are expected to enforce MY values and rules, which are pretty clear!! Should a parent choose not to, I absolutely will.
For whatever reason, kids tend to go nuts at pick up. Maybe overstimulation, excitement about seeing mom/dad, a little bit of anger that mom/dad have been gone all day.... I don't know.
And for whatever reason, parents don't tend to discipline the kiddos. Guilt over being away all day, embarassment, maybe it just never happens anyway (the discipline).... I don't know.
But I have told this story once, and I will tell it again. I used to be all casual and let mom/dad deal with all the behaviour. Probably just non-confidence on my part. That ended the day that a 5(!) year old boy KICKED my front door into the wall, because he didn't like what his dad told him they were going to have for supper. No more Miss Nice Lady.
From that point on, if YOU aren't going to show/teach your child, I WILL. As long as they are around me, they will behave in the manner that I expect from them.