What does it mean to "receive the kingdom of God like a child"?

One day people bring children to Jesus to bless them. The disciples oppose them. Jesus is upset and instructs them to let the children come to him. Then he says to them: "Whoever does not accept the kingdom of God as a child will not get in" (Mark 10: 13-16).

It is good to remember that some time before, Jesus said to the same disciples: "You have been entrusted with the mystery of the Kingdom of God" (Mark 4:11). For the sake of God’s kingdom, they left everything and followed Jesus. You are looking for the presence of God, you want to be part of his kingdom. And now Jesus makes them understand that if they reject the children, they will shut the only door to the longed for Kingdom of God!