The scribes were treated with excessive deference in Jewish society because of their education and learning. Everyone honored them because of their wisdom and intelligence. The "mere children" (napioi in Greek, really meaning babes) were Jesus' image for the uneducated and ignorant. He is saying that the gospel of grace has been disclose to and grasped by the uneducated and ignorant instead of the learned and wise. For this Jesus thanks God.