1 Tim 3:14-16 / Luke 7:31-35
As much as there is a difference between childish and child-like, most of the time, it is the childishness that is most prominent.
When Jesus was looking for a description for the people of His generation, He used the analogy of a children's game.
When children play games, they expect everyone to play by the rules. So when they play pipes, they would expect others to dance, and when they sing dirges, they expect others to cry.
So even children have their expectations and when those expectations are not met, they will become childish and start complaining or throwing tantrums.
Jesus and John the Baptist did not meet the expectations of the people of their time and the people called them names like "possessed" and "glutton" and "drunkard".
Even though the people are adults, when they are not matured with wisdom, then they can be really childish and begin to call others with derogatory names.
As it was then, so it is now. When people don't mature with wisdom, they become childish and not child-like
In the 1st reading, St. Paul tells Timothy that he wanted Timothy to know how people ought to behave in God's family, that is, in the Church of the living God, which upholds the truth and keeps it safe.
Spiritual maturity enables us to have a child-like obedience to the truth, so that we won't succumb to childishness and complaining and calling others names.
May we also live out that truth with love and be witnesses of God's wisdom to our generation.