Well, lots of things can be responsible. I recommend replacing all peanut products with almonds and soaking almonds to make them like they are fresh from the tree and full of water and easy to digest.
Almond butter is healthier than peanut butter.
I hate most legumes, but well-cooked lentils and green peas are pretty easy digest for me, whereas soy products and kidney beans and garbanzo beans give me gas and wear me down. I hate tofu. And last but not least, while here in America they tell people to eat fruit at the end of the meal, it's probably better to eat plenty of fresh fruit first and then some more concentrated plant foods. A lot of people stuff themsleves full of grains and then find they have no room for fresh fruits and salad. Why not indulge our kids penchance for finger food by providing lots of fresh berries and delicious peaches and kiwis for them rather than trying to force them to eat brussel sprouts or giving them cookies.