Kids are pretty resilient. What you do for your child day in and day out is by far the most important. I made the mistake when my daughter was young in the 70s, and I was then in a big vegetarian phase, of not allowing the occasional "kid" food (like a Happy Meal), and it took until the 2001 when my twin granddaughters were born for her to begin to want healthy foods. Obviously, if children have health issues, most people are respectful of the child's dietary needs, but that still requires a considerable amount of parental monitoring. If your precious one is healthy, doesn't have any allergies, etc, the occasional PBJ or Oreo is not going to have much of an impact. As someone once said: It's not what you do 15 days of the year, but what you do the other 350.
This time, like all times, is a very good one, if we but know what to do with it. Ralph Waldo Emerson
Any given day you are surrounded by 10,000 idiots. Lao Tsu, founder of Taoism