Jesus said to let the little children come to him, because the kingdom of heaven belongs so such as them. Children can have a very profound and simple trust in God that can be our guide when we feel our faith flagging.
Based on Matthew 19:13-15:
Little children were being brought to Jesus in order that he might lay his hands on them and pray. The disciples spoke sternly to those who brought them; but Jesus said, ‘Let the little children come to me, and do not stop them; for it is to such as these that the kingdom of heaven belongs.’ And he laid his hands on them and went on his way.
(New Revised Standard Version Bible: Anglicized Edition, copyright © 1989, 1995 National Council of the Churches of Christ in the United States of America. Used by permission. All rights reserved worldwide. http://nrsvbibles.org)