K.,
Have you and your husband sat down and discussed your concerns about your son? Does your husband think there is an issue or not? If he doesn't, you can't make him change his ways but I assume that you are "in charge" of the menu, right?? You can make the changes needed, just don't make it an issue. If he does think it's an issue, does he realize that his son will want to mirror him? and doesn't he want what is best for his son?
Just to share with you what my husband is dealing with at 34 years old: He's 6'4" and weighs almost 300 lbs. When he was 9, his father (who is a doctor, mind you! grrr) put him on a diet. He made exercising a chore and made food all the more alluring by taking anything that tasted good (candy, cookies, etc) away, therefore, forcing a 9 y.o. boy to horde food in his room. To this day, my husband has food issues. He doesn't know how to eat right and doesn't know how to do portion control. He feels like working out is "work" and although he knows he should do it, doesn't like to.
So, my advice to you would be to slowly modify your and your family's diet. Buy healthier cookies/ice cream and adapt the "anything in moderation, nothing in excess" motto that we follow in our home. I find that if I take the snacks out of their original package and break them up into separate ziplock baggies, we don't eat as many in one sitting. And buying only a 6pk of sodas instead of a case at a time. It took me three years to get my husband to stop drinking ONLY coffee and diet sodas...but now he drinks water mostly, one or two cups of coffee a day and maaaybe a soda a week with lunch.
I understand about cooking not being your thing...I'd much rather go out to eat myself...but I have found that Rachel Ray and her 30-minute meals are FANTASTIC! Easy and delicious. There is another lady on the Food Network that does "Semi-homemade" things...her recipes are good, too. One more cookbook that I have is from a series called "Gooseberry Patch"...easy and tasty and most ingredients are things you'd have in your pantry.
The other thing is, since your son is nearing puberty...which could be a cause of the weight gain...instead of making food an "enemy", take walks with him, get outside and play active games. Go biking together, etc. make exercise fun. It won't hurt you or your husband and it will make exercise more appealing to your son if it isn't "hard" and is a family activity. If your husband doesn't want to get on board, fine. Just make the decision for you and your son and stick with it.
Basically, the way I look at it is that if you do the grocery shopping...you're in charge of what your family eats. If your husband refuses to give up the sodas, etc. Fine, but they don't need to be available to your son...grown ups do a lot of things that kids shouldn't.
And to add that I am not giving my advice without thought, my son is 10mos old and outweighs his friends who are 2-6 months older than he...he's 25lbs! So, I have the same concern for my boy which is why I am trying to make the dietary changes now! :)
Good luck and I hope that knowing my/my husbands situation helps!