Hi K.. I'm sorry you and your grandson are having such a hard time with food. I'm including two links for you to consider reading. The first explains about the mineral zinc. An alternative health care professional I know and admire told me a long time ago that anorexic's suffer from a zinc deficinecy, give them zinc and their appetite comes back. This is a problem with seniors who lose their appetite as well.
Secondly, acid reflux is not too much acid but too little. That is why the pills didn't help, they supress the acid. How can you process food without enough acid, you can't, and it makes eating quite painful. A way to help his digestion is to make bone broth. I know it sounds weird....however, it will benefit him in ways you never imagined! The second article is all about bone broth, what it does, how to prepare it etc.. Once you make it, you need to substitute broth for any water you need to prepare his food. Cook rice with it, noodles, make soup etc.. Bone broth is a time honored forgotten remedy for malnutrition. You want all of his vitamin and minerals to come from a food source, not the fortified man made garbage. When the label says 100mg of something, your body only uses a fraction of it and has to deal with the waste product and stores them in your cells. This leads to unhealty cells. Please try to buy your bones from organic raised animals, especially chicken because regular store bought ones will not gel. I know I've tried. You need it to gel. If you live near Ann Arbor there are plenty of sources there. Arbor Farms, Sparrow Meats or Whole Foods.
The brain is mostly fat and needs healthy fat to develop properly. Carlson's cod liver oil (lemon flavored) can be added to his food and he won't even know it. I say cod liver over fish oil because of the vitamin D, we in the north need a lot more of it because of our long winter season. This is a very inexpensive way to feed the brain.
I hope I haven't rambled on too long. Here are the two links:
http://dietary-supplements.info.nih.gov/factsheets/cc/zin...
http://findarticles.com/p/articles/mi_m0ISW/is_259-260/ai...
I wish you all the best in your quest to better health for your grandson.
H.