Mathew 18:3 and 19:14 and Mark 10:15. Seems like I`m unable to past it here, but you can just google it and find those. Obviously, to say Jesus ment AB`s by what he said would be perverting the words, but as far as I believe what he did mean was that a child`s innocence and willingness to have faith (children have faith in their parents or guardians). If there are any spiritual roots to AB´s, then this is it. Our wish to return to that time, in many cases at least, has a wish to be relieved of responsibility and worries of life. Responsibility is a fruit of having the ability to make decisions, so a child`s innocence comes from being too unware to be truly held responsible for their mistakes, while having faith would relieve you of worries in life, in a way I will not be explaining now.