This was a person who did day care out of her home. At the time, she only had my 2 girls plus a couple of her own and I found out several months after the fact that she had been taking them out to McDonalds for breakfast or lunch two or three times a week (she had my permission to take them on outings such as to the zoo, etc...).
I started to wonder when they were 2 and 3 and started recognizing "The Golden Arches" whenever we passed a McDonalds even though I had never taken them there.
While I do allow my girls to eat junk food on occasion, I really try to emphasize putting "good fuel" in their bodies and work with them on learning what good choices are. My oldest has a terrible sweet tooth (inherited from me, no doubt), but my youngest will often eat only half of a dessert and then walk away from it.
In another year or two, they're going to be old enough to start helping me plan and make meals and that will really provide a good opportunity for teaching healthy meals and eating habits. All in all, I'd still say that modeling is the best way of teaching. They see what my DH and I eat (and don't eat) and it makes an impression on them. Kids will more often model what you do than what you say.