I'm beginning to think that this issue is something that only a preschool teacher can appreciate!
When I was pregnant with DD, I was treated as a borderline Gestational diabetic. I had to watch what I ate, and it caused me, over time, to change my eating habits. Once DD, started solids, I made her own baby food, and simply decided that she didn't need to eat that crap.
However, because she gets little of that stuff at home, I do relent when it comes to a school party or birthday party -- it's not like I'm going to tell another mother at a birthday party "You know, you should really serve more healthy stuff for the kiddos....."
At DD's birthday parties, I get accused of going all out and making too much, but there are family members who attend who can't eat x, y, and z have high blood pressure, diabetes, etc. So I make lots to give people options. Typical fare includes: hot dogs/hamburger/veggie burgers/baked beans/pasta salad (loaded with crisp veggies)/fruit salad and then the cake and ice cream. DD will usually eat 1/2 hot dog (no bun), pasta salad, pickle, and fruit. Later we let her enjoy the cake and ice cream. Tonight we went out to eat and our waitress was awestruck when DD(3) ordered herself a house salad and baked potato with cheese. She listened as DD repeated her order and then said "Is that what she really wants?" She expected DD, like most kids, to eat chicken nuggets or mac-n-cheese. Nope, I've raised a good eater (although we do allow her to eat chicken nuggets when out).
I allow balance. I am not opposed to having snacks and sweets in the house. The past two weeks we've had Halloween candy to nibble on, so she gets some candy after dinner. I do keep things like cereal bars (Nutri-Grain), gummy fruit snacks, and goldfish crackers around. I keep a snack basket in a lower cabinet that DD can get stuff at will. You woul dthink that she would just eat and eat since she has access to it, but most of the time she just takes one snack.
Anyway, when it comes to daycare parties, because I know that cookies, chips, cupcakes, and such will be served I usually make something with some protein for balance. This year, I am an exception.