I treat this verse as a single sentence paragraph. The vocative case of address, “My little children,” also marks this verse off as a paragraph. The point of the verse is to present something of a summary exhortation based generally on the entire letter and specifically on the conclusion of the previous paragraph, stated in v. 21, that Jesus is the true God who gives eternal life to all believers.
The structure is something along the lines of grounds – Exhortation:
A. Since Jesus is the true God,
I. Don’t worship false gods (idols).
In other words, accept no substitutes!