Paul is referring to a process of spiritual maturity that will keep us solidly grounded and on a steady course to the Kingdom of God.

Two of the phrases Paul uses in this passage deserve expounding by commentator Albert Barnes:

[That we henceforth be no more children] . . . children have other characteristics besides simplicity and docility. They are often changeable (Matt 11:17); they are credulous, and are influenced easily by others, and led astray. In these respects, Paul exhorts the Ephesians to be no longer children but urges them to put on the characteristics of [adulthood]; and especially to put on the firmness in religious opinion which became maturity of life. . . .

[And carried about with every wind of doctrine] With no firmness; no settled course; no helm. The idea is that of a vessel on the restless ocean, that is tossed about with every varying wind, and that has no settled line of sailing.

As we know, children have short attention spans; they change directions seemingly in an instant. They will begin to play with one toy only to be distracted by another a moment later. A parent will tell them to do something, and the intention to obey escapes them as soon as something else comes up.

While Jesus tells us that, in our conversion, we are to "become as little children" (Matthew 18:3), He is not referring to this kind of simplicity, changeability, and distractibility. Putting these two admonitions together, Christians are to be mature in their convictions and faith, yet open and humble as little children. In this way, they are receptive to God's truth and the guidance of His Spirit, yet sure and uncompromising in their beliefs.