I've had that too - at one time I used a Treasure Box as a bribe for the children to go home nicely!
One thing I do early in the relationship is find a time to casually mention that all children go through a phase where they don't want to come in the morning and don't want to go home at night. I'll talk about it a couple of times, then when the child reaches the phase the parents are fore-warned. IMO it's better to let them know at a time when the child ISN'T going through it than wait until they do - if you wait it looks like you're making things up so the parent won't be upset.