As a mom, I understand your worry completely. I would imagine if it was a food related illness all the kids that ate them would be sick. Did you say just 1 of the kids are sick?
I guess it wouldn't hurt to call their pediatrician for peace of mind, if anything. They will be able to explain more of what to look for. Also, at least for me, it helps calm me down just knowing the doctor is aware of the issue.
Hope your baby feels better soon!