Regarding Matthew’s narrative, it is plausible that the disciples were initially quiet until one of them took the initiative to ask the question that was on everyone's mind.
In response to their query, Jesus, as reported by Mark, initially articulated the fundamental principle of interpersonal relations within His new kingdom: "Whoever desires to be first must be the last of all and a servant of all." Following this, He positioned a child among them and, as Mark notes, embraced the child, teaching that the qualities of children—such as their unselfconsciousness, lack of pretentiousness, and innocence regarding social status—serve as the essence of the Christian virtue of humility. This quality is essential for true members of the kingdom of heaven.
Subsequently, Jesus instructed His apostles on how to treat children and outlined the proper demeanor they should adopt towards them, stating, "Whoever receives one such child in My name receives Me." By this, Jesus not only refers to natural children, who are indeed vulnerable and have not yet earned merit before God through faith and good works, but He primarily emphasizes the attitude of the apostles toward spiritual children—new believers who, like natural children, may be weak in faith and not yet fortified in deeds of piety.