How to ask family to not bring any food to daughter's 1st b-day party?

I have sent out an evite.com email inviation for my daugther's 1st birthday party. It is family and about 25 people have been invited. The party starts at 4:30. We are serving meat, pasta salad, cheese bread, chips and dip along with cake and ice cream. Some people have asked what they can bring which I understand and appreciate as the polite thing to do. How do I politley ask them to not bring anything (food wise). We wanted to keep it low key and what I'm serving seems like enough to me. How should I ask them to not bring anything without sounding rude?