My son needs to lose weight?

Educate him about what he is eating and what it can cause. Also don't buy as much junk food but when you do, hide it and only give it to him once in a while. It sounds kind of like he thinks it's funny to be that way or thinks it's not much of a big deal. No one ever taught me about eating healthy and exercise, and still don't, ( I'm 16) so I had to find my own way exept for my mom buying me a membership to boxing classes and now I'm doing doubles in p90x (an extreme full body workout). The good thing is, is that you are willing to help him. If you want to make it easier for him then you should diet with him even if you don't need it, so he won't go through it alone. Buy lots of different fruits and see which ones he likes, like watermelon, strawberries, mangos, pears and many others. You can also make them into juices and put some fiber into it to make him feel full.