It's pretty easy to assume your kids are getting the right kind of food when you don't really pay attention to diet in general. Kids can live off junk food for a long time, but it doesn't do their health much good.
I believe that children shouldn't be forced into eating things that they truly don't like, but I also think that they tend to eat the things their parents eat. So if you don't want your kids to make themselves ill by eating too much pizza, you have to set the example by having meals with lots of vegetables and protein with them more often.
Nothing is more annoying than a parent who claims their child won't eat their vegetables, when they demonstrate poor eating habits to their child all day, every day.