I also find too, that at the end of the day, some little ones are sooooo overstimulated (not to mention tired) that they just "spin out". They are excited to see mom/dad, but have been having fun so they don't want to leave, either. They've been playing so hard, that they are just DONE IN. That tends to manifest as utter meltdowns. It's hard for moms and dads, to see the little person who should be running into their arms having a tantrum. And no less hard for providers!
But consistency, patience and continuing to enforce the house rules (no hitting, no tantrums) will ensure that it gets better eventually.