NOTES for Mat 18:1-14
The evangelist connects the words about the children we must become in order to enter the Kingdom of Heaven with a small parable about a shepherd and a lost sheep, and this immediately puts everything in its place. The point is not only that we become weak, defenseless, and dependent, although at times we really do need to feel like children before God; Christ is clearly speaking here about a "new childhood," that is, about a second birth - not only about feeling like children in comparison with God, but actually becoming children of the Heavenly Father (and here any childishness is out of place; this calling is too high).
Understood this way, the familiar commandment "be like children" becomes an incomprehensible call to become participants in God's life, to become beloved sons and daughters in the beloved only-begotten Son - the path opened before us in Christ's Resurrection...