They claim to be non-toxic,in small doses. However, large amounts can make you sick. But if anything glows the way a glow-stick does, I feel like there has to be something dangerous in it. If he feels sick later that night, don't hesitate to take him to a doctor, and tell them that he ate a glow stick. Tell him not to make a habit of it.
Call posoin control immediately. My brother pooped one when we were camping when he was sleeping and it burned his eyes my mom was freaking out he had to keep flushing it out with water. If it can do that to your eyes I can't imagine it being good for your insides.