I have had kids melt down at pick up time for different reasons

1- They want to show off in front of their parents or are craving for attention and therefore act up or they are testing the boundaries between the parent vs daycare provider

2- They get an emotional meltdown because they can't process the emotions involved and the transition from saying bye to the fun/friends at daycare and the excitement of seeing their parent return.

I would make a comment to the child and say 'we don't put the keys on Mambia's wall"