I know that it is hectic getting out the door in the morning for work with little ones but I have a family who give their son breakfast in the car and then he brings it in my house in a baggy even though it's against policy. Thing is, I think what happens a lot isn't just poorly organized households but this particular family have told me flat out that he looked so peaceful sleeping so didn't want to wake him. But then they are rushing out the door without a proper breakfast at home. Makes me shake my head that they have such little thought and consideration to dcproviders who have multiple children and don't care about breaking policies.
To the OP....I think amending your contract with very clear terms that breakfast is neither provided or an option is very important. Also just adopt a strict no outside food policy so that bringing breakfast in is not an option. I put it down to allergies so I can additionally add that children's hands and face need to be thoroughly cleaned prior to entering daycare. On top of this written notification I strongly believe that there will always be those families who still don't get it. You have to talk to these people face to face and have them acknowledge it. Don't even begin to assume that just because you have put it in writing that they have "got it". I gave up on common sense a long time ago.