This is what I thought the article was saying until I read it. But if most babies are cradled on the mothers left, that would lead to the babies left side being more interacted with by the mother. Since most sensory information is processed contralaterally you would think it would bias towards left-handedness by strengthening connections in the right brain which is clearly not the case.

However, smell (and taste, but I don't think that is relevant here) is processed ipsilaterally and vision/hearing have some ipsilateral processing so maybe I am wrong and it IS strengthening their left brain and leading to right handedness.

Wouldn't that mean all/most siblings have the same handedness?