A baby cow will suffocate if they only have a one block height to stand in. Normally, adult cows have a height of one and a half block, and baby cows only have a height of one block. The baby cow hitbox is probably replaced by the adult cow hitbox. The same bug applies with baby mooshrooms. It does not apply to other mobs like sheep for example, who just like cows have adults of one and a half block height and baby's of one block height.