Jesus answered them. He had it exactly backwards. Earning admission into the kingdom of God is NOT possible. But being acceptable to God IS possible through God's mercy, through God's forgiveness, through God's unconditional love. The passages that come before this one shed light on the rich man's story.
Children know how to receive gifts.
Adults want to earn their way. We have the children who Jesus invited to come forward and the adult who has kept all the commandments set before us side by side. You couldn't make a much sharper contrast. The children enter. The responsible and obedient adult is turned away.