Jesus used little children on different occasions as object lessons to teach different lessons. Once He used a child to teach that no act of kindness for one of His suffering disciples, whom the child represented, will pass without God"s reward ( Matthew 10:40-42). On the present occasion Jesus used a child to illustrate two lessons. By standing the child beside Him Jesus gave the child honor. Mark wrote that Jesus took the child in His arms ( Mark 9:36). Evidently Jesus did both things. [source][source][source]
The first lesson Jesus used this child to illustrate was that His disciples should be as humble as little children ( Matthew 18:4; Matthew 18:6). Luke did not mention that lesson. The second lesson was that acceptable service involves caring about people, even insignificant people such as children ( Matthew 18:5; Mark 9:37). That is the lesson Luke included in his account of this teaching ( Luke 9:48). It reflects his interest in neglected people. A child was the least significant person in Jewish and in Greco-Roman culture. [1][source]
Jesus meant that instead of seeking status for themselves His disciples should give their attention to the needs of people who have no status, people like children. The disciple who ministers to a person with no status as though he or she was ministering to Jesus does indeed minister to Jesus and to God the Father. The principle is that the disciple who is willing to sacrifice personal advancement to serve insignificant people, as the world views people, is truly great in God"s estimation (cf. Matthew 25:35-40; Mark 9:41). [source][source][source]