12 I write unto you, little children, because your sins are forgiven you for his name's sake.
The "Little Chldren the Apostle John is referring to here are NEWLY born children of GOD. New believers who have just entered into the faith and accepted Christ, knowing nothing else other than by faith they have believed on HIS name and accepted HIS payment for their sins!
John is encouraging them here and letting them know he is writing to them and giving them a little bit of knowledge of the faith and life in Christ Jesus!