K.J.
Chamomile, meadowsweet, fennel and ginger root are commonly recommended for GERD treatments. Try one at a time until you find what will work with your little boy. Great American Bulk Foods Store on 16th Street North in St Pete between Haines Road and Iris Street has all these in capsule form if he can swallow that or you can open the capsule and sprinkle it on his food. They have the freshest of all herbs and are an old time apothecary.
I would try the ginger first... you can serve it with honey and teriyaki sauce (glaze fish or chicken with it) and also mix it with oj and garlic cloves for another awesome flavor. If you are interested in recipes let me know. If you just want the capsules Great American is the place to go. (Dee Dee is my favorite person there!)
Hope this works!
KJ