Sounds like it's time for a total daycare policy review by all the parents ... as a mommy, sometimes we develop relationships with our daycare providers that crosses over into friendship, and sometimes it's easy to unintentionally take advantage of that relationship without really meaning to, and we need to be reminded of the fact that while we might be friends, there is also a contract between us pertaining to care for our children.
I suggest you draft up a reminder doc for all the parents to include a reminder of the drop-off policy (if you're not coming, please call); meal times (if your kid isn't here by 9 a.m., you better have served them breakfast, and a bag of M&Ms doesn't equate to breakfast
); pick-up times (and the per-minute fee for being late); that children are expected to be bathed and otherwise clean when dropped off; don't bring your kids if they're sick (to get the others sick); etc. Reiterate that your priority is the health and safety of ALL the kids, and include on the letter that this is a friendly reminder to ALL parents.