What things is he referring to? Those things he has just written. So, it's not possible that his letter did not include Christians he consider his "little children".
John 16: he will reprove the world of sin, and of righteousness, and of judgment: 9 Of sin , because they believe not on me; 10 Of righteousness, because I go to my Father, and ye see me no more; 11 Of judgment, because the prince of this world is judged .
He reproves the "world". He also loved the world so much he gave his only son. We are part of the world.
Moreover, "Of righteousness" is directed to "Ye" (You all) who would see Him no more". That is, the disciples/apostles to whom he was then speaking.
Do you believe that you do not sin?
Of course I sin, but in the New Covenant in his blood, God declares, "their sins and their iniquities will I remember no more" Heb 8:12. As the gospel of the grace of the Lord Jesus Christ declares and as I have repeatedly said here, ALL of our sins, past, present,and future were thoroughly judged 2000 years ago, God exhausting all condemnation of ALL of our sins on His Son. Our sins were transferred to the Lamb of God and His righteousness was transferred to us in a divine exchange by His AMAZING grace ("It is finished").
So you and I sin, but we are already forgiven. You may ask, like those who asked Paul, "Shall we therefore sin that grace may abound?" (Rom 6:1). But Paul's answer was, "Sin shall no longer have dominion over you, for you are no longer under the law but under grace" (Rom 6:14). Grace, not the law or self effort, delivers us from the bondage of sin.