Maybe because they've had so much of it that they've developed allergies?
Kind of like how if you consume too much dairy product, you can become lactose intolerant.
Too much bread and you can potentially become gluten intolerant.
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There was a pervasive and incorrect myth that children under 1 year couldn't eat peanuts or its byproducts. Actually that's the best time so thier immune system can acclimate to the stuff. Best to wait until 6 months. Please verify this... mainly because I think I am wrong and it's the 1 year to 2 year period