Objects continue to exist when we don't see them. Other people have thoughts that are different from our thoughts. Water does not change its amount when poured from one container to another. Language. Children, at different ages, do not have the physical capability of understanding these facts. It isn't that they are miniature adults who have yet to learn things. They cannot learn these things, cannot act on them, cannot perceive them in others. Later, they can. Infants and children are cognitively distinct from adults. There is a change from infant to child to adult (for the lucky), but they are not all the same. Something I keep in my mind when I read people write what is best for all people regarding rational thought. The cloud of ideas that is rational thought is not evenly distributed.