Jesus proceeded to describe the Jews' reaction to John and Himself more fully to clarify their opposition.
11:16-17 The generation Jesus spoke of consisted of the Jews to whom He offered the kingdom (cf. vv. 20-24; 12:39, 41-42, 45; 16:4; 17:17; 23:36; 24:34). Jesus must have observed children playing the marriage and funeral games He referred to here, and He used them to illustrate the childish reaction of most of His adult contemporaries. The point was that the people found fault with whatever Jesus did. He did not behave or teach in harmony with what they wanted Him to do or expected that Messiah would do. His concept of the kingdom was different from theirs. They wanted a King who would fit into and agree with their traditional understanding of the Old Testament. Consequently they rejected Him.
11:18-19 Even though John lived as an ascetic, as some of the Old Testament prophets did, most of the Jews rejected him and even charged him with demon possession. Jesus ate and drank with sinners, and many of the people criticized Him for lack of moderation and concluded that He despised the law. If they would have understood John, they would have understood Jesus.
Jesus concluded with a proverb that justified John's and His lifestyles. The Jews had criticized both John and Jesus for the ways they lived. Jesus' point was that the good deeds that John and Jesus did vindicated their choices to live as they did. Who could justifiably criticize them since they went about doing good? Wisdom in the Old Testament is almost a synonym for God in many places. Jesus claimed that He and John were living wisely, under God's control, by behaving as they did. The Jews could make childish criticisms, but the lifestyles of John and Jesus argued for their credibility.
In spite of John's doubts Jesus supported and affirmed His forerunner to his disciples and his critics. John's message was correct even if he had developed some misgivings about it.
