Good point.

Maybe this "greatest" lesson is why Jesus asks us to approach Him like a child.
Maybe it means a less developed and influencing ego. 
An openness to being shown.
Fewer defensive barriers.

Simplicity, sincerity, humility,  openness, trust.

Spiritual childhood is a developable virtue and habit of mind that can help us remain easy to be helped by a loving Father God. 

A good spiritual director can help adults regain their active sense of spiritual childhood, looking at all moments and events more calmly and trustingly.   Efforts in living out (and knowing about) spiritual childhood can create a spark of joy in one's life that can be fanned with prayer and powered by grace from the frequent reception of the Sacraments.   Receiving Communion on the tongue can even increase our child-like disposition to be helped by God, spoon fed once again.