Mark 9:36-37

To enforce his teaching, Jesus called for a little child who was in the home where they were staying and, taking the child in his arms, he said to the disciples, Whoever welcomes one of the little children in my name welcomes me; and whoever welcomes me does not welcome me but the one who sent me. (Mark 9:37)

Jesus was illustrating the timeless truth to his disciples. He was not simply saying that they should be kind to children, though that is involved. He was saying that his followers must be willing to render service to any individual, even though there is little possibility that such an individual can in any way repay that kindness. We manifest kindness to a little child, not with thought of reward, but because we instinctively love little children and wish to be of help to them. This is the attitude that the servant of Christ should have to all who are weak, or helpless, or in need. When we habitually take such an attitude towards the world because of our relationship to Jesus Christ (in Jesus's name) we render service to Jesus Christ and to God.