Originally Posted by CountryRoads:
Why do kids act up so bad when their parents are here??
They can be good all day, then as soon as they see their mom/dad they lose their minds. They break my rules (which they can follow all day), they don't listen and then I have to step in and parent because their actual parents can't do it themselves - which then leads to crying, screaming, etc.
What makes it worse is the parents try to reason with them. Please, just grab your kid and get out!!
Drives me crazy 
Just practice saying that...
"Hey mom/dad, since you aren't going to enforce my rules, please take Johnny and go to the car. I'll see you in the morning."
I've found that calling them out pushes them to parent their kid or leave quickly....either way it's a win for me.
If the kids are old enough (3+) I also have a reward chart for those kids that are well behaved at pick up. They get to choose their activity first the next day etc... positive re-enforcement for their good behavior the night before. That helps alot...especially for those kids that are motivated by rewards.