I didn't know that either until after i ate them when i was nursing DS1.
Legumes are also in the same family as peanuts. So if your LO has a peanut issue, there is a chance he may be allergic to some or all legumes. Crazy -i know!
But it sounds like it's the soybean that's causing the issue. But a legumes allergy is pretty common..
btw -love your siggy pic! too cute