Try giving him a glass of water with lemon in it have him drink a little before his meal (and even with it). There is a sweetener called Stevia. It is the only truly natural sweetener on the market. It has no calories and it does not feed yeast. BUY IT! The brand I like the best is "NOW' The Whole Foods Market has it. It's concentrated so you only use a pinch. Take a glass and sqeeze a half of a lemon into it. Then use a tiny bit of stevia to sweeten it (nothing else). Give this to him with his meals. If it helps with the burping, even a little, he has too little hcl.
By the way, I'm a Nutritionist :)
It could also be that his stomach does not produce enough hydrocloric acid. If I were you, I would go see a Holistic Medical Doctor. Only this type of doctor can test for things like yeast over growth and too little hydrochloric acid.
Cute kid : )
It MIGHT be that he has too much yeast in his system. That is, too much bad bacteria in his gut and not enough good, probiotic bacteria. Certain foods ferment in the system when there is too much yeast, and this causes bleching and/or gas. The worse culprit is sugar. All types of sugar including fruit and fruit juice. Next is fermented foods like pickles, mustard, vinegar, breads made with yeast, etc. And all white refined grains like white bread, white noodles, white rice. He would need to come off all that and start taking a probiotic and a digestive enzyme. Primal Defense is the best probiotic on the market. It's made by Garden of Life. They may make capsules for children. Don't get the powder or tablets. They also make a great digestive enzyme called, Omega Zyme. Check these things out on the web. Also, there is a tiny little book that is very easy to read called, The Bible Cure for Yeast and Candida, by Dr. Don Colbert. Read it and follow the instructions. You can buy it off his web site. Good Luck!