I do home childcare (over 14 years) and spent the 10 years before that as a nanny for a pair of Dr's and working in a health clubs child center. I have seen my share of barf.
Parents are not "dumb" just like caregivers are not. We generally know the difference between the "coughed so hard he yakked", or "slammed the milk so quick it came back up". If they ate too many sweets..too bad, my rule sticks. Someone should have been in charge of the sweets bin! My job description is truly not to clean up every single bodily fluid a child can produce. My house would be even more destryed and barf is a place where I draw the line.
I have a 24 hour rule, just like the schools here go by. Its for fevers and barfing and I am very very strict about it. I get sick fairly easily myself, and some kids are just like me and not as hardy and catch everything. Its not fair for you to knowingly expose everyone else in care to whatever it might be, just because you do not have back up care in place and need to get to that meeting. I am very clear with parents about these sorts of policies at intake interviews and I hold steady to them. I also have hefty fees in place if I do have to call a parent and they do not have the child picked up within an hour of my contact with them ( plenty of time to come from downtown, arrange schedules, grab a bus if needed, etc). Backbone 101!
BTW~ I DO run a very succesful, waiting list at most times, home childcare. Most parents applaud my no nonsense policies like this.
Best of luck to you!!!