S.T.
you can't be 100% sure, but does it matter? the treatment is basically the same, and you probably need to enlist help anyway.
for me food poisoning was more violent and horribly uncomfortable than even a bad stomach bug, but i'm not a doctor and don't know if my experience is typical.
short of getting lab testing, the only sensible way to diagnose food poisoning is to scrutinize what you've eaten lately. if it's at a restaurant and you really think it could have happened there, of course it's a great public service thing to alert them to the possibility so they can check it out.
but when the pedal hits the metal you just treat it until it passes. i'd definitely keep it away from the baby regardless of the cause.
khairete
S.