It sucks when they're not feeling well. You did everything you could at drop off this morning.

Maybe mention at pick up that he was really difficult and if he is not feeling well enough to participate in activities then it's not fair for him to be dropped off.
At a centre, she wouldn't have dropped him off. But because she comes to your house there's this sense of "she'll take care of my baby" It's still not one on one care like some parents perceive, it's one on 5 care in most cases.

I hope he's not overtired and doesn't sleep well. I hope you have a good breat today. And if not, call that mom and get her back there. Not fair to you!