It is a big deal. Your daycare does not serve breakfast whether it is brought in or provided by you.
You, as a provider, are not there to do the parents job aka preparing their children for their day by dressing and feeding them. It is not fair to the other children to see food being eaten by their dc friends and not being allowed to join in.
You need to tell them that you do not provide "breakfast time" and it impedes the flow of your daycare schedule. The parents then need to suck it up and get up earlier and feed their children. I find the clients who are soooooo nice are the biggest perpetrator's of trying to take advantage or not follow the daycare policys and they are also the ones who can turn nasty if they are told no. Bottom line, you are not the "help" you are a business person who runs a daycare and your policies and schedule need to be followed.