מדרש על קידושין 71:27

(Ibid. 14:1) "Children are you to the L-rd your G-d": R. Yehudah says: When you deport yourselves as children, you are called "children"; when you do not deport yourselves as children, you are not called "children." R. Meir says: In either instance you are called "children," as it is written (Jeremiah 4:22) "They are foolish children," and (Ibid. 32:30) "children without faith," and (Isaiah 1:4) "seed of evildoers, perverse children," and (Hoshea 2:1) "Instead of being said of them, 'You are not My people,' it will be said of them 'children of the living G-d.'"