If you try to change your diet in one huge go, from lots of junk and no veggies to lots of veggies and no fun, your kids are going to notice. And they won't like it! If you make small changes, little by little, you'll find it much easier to sustain and your kids will probably not even notice. Pop over to Youtube to see the video.
P.S. I was joking about the fun! You can still eat a healthy diet and have lots of fun and treats.