How awful for your son, and for you. I wish I could tell you that a vet could help, but I don't think they could. A condition called hepatic lipidosis sets in after 12 hours of no food, and there is no cure for it.
I'm going to give you a couple of things to try. I have to be honest with you, the situation looks grim, but it may help Charles to try to help Fluffy. And, who knows, maybe his love and caring will result in a miracle. You can get some Pedialyte (yes, the same you use for kids). Us a syringe to put a little in the side of Fluffy's mouth. You can do this every ten minutes for the first hour, then once an hour after that. You can add a little liquid vitamin C in with the Pedialyte. There's a special food called Oxbow Critical Care that you can buy in larger pet stores. It is fed with a syringe, too. You can also make a slurry of crushed pellets, water, and pureed vegetables. This can be more difficult than it sounds, so I'm giving you a link to a page that describes it in great detail, including variations on what to feed, and how often to feed:
I don't want to give you or Charles false hope, but I do feel that as long as there's life, there is at least a glimmer of hope, If Fluffy should happen to respond to these measures, then you might want to consider taking her to a vet. I suspect that if you took her to one now, the vet would recommend euthanization. Regardless of what happens, your son may feel better if he's actually doing something to try to help. If money wasn't tight, I'd tell you to go ahead and see a vet, but I hate to recommend that you spend your hard-earned money on something that only has a slim chance of being successful. The steps a vet would have to take to try to help Fluffy would be quite expensive. You'd probably be looking at hospitalization, with fluids and tube feeding, medications, and even surgery if the teeth are involved.At age five, these measures aren't likely to be successful. Only you can make the decision as to whether you want to try all of that.
This is truly a heartbreaking situation. I can't even imagine how hard it is for you, as well as Charles. If you need anything else, don't hesitate to let me know.