There is much in spirituality that refers to becoming "like a little child" or becoming little or small. I think it is more accurate to speak of being a child or being small, rather than becoming.
The fact is, we are small, we are all but nothing. From God's perspective, we are "like ants" seen from a great height. He is all, we are not all. He is, by nature. We are not, by nature. God has no beginning, no origin, no originator. He simply is, and he is all-powerful. He is perfectly simple, being all in all, without parts, without any division, he is perfect unity.
We have an origin, and an originator. Without the sustaining will of God, we could not continue to exist. We are entirely dependant upon God for simply existing.
Everything about us, everything that are, have, hope for, depends entirely on God. So being a child, being little, is simply a matter of being true to what we are, simply acknowledging our relationship with God. It is not a matter of becoming something, but of accepting the truth and not trying to be something that we are not, and that we cannot be. It is a matter of not trying to be more or greater than we are. It is a matter of living the reality of who and what we are, in relationship with God's reality of who and what he is.
It is a matter of living the truth, as simply and as humbly as we can.