Christ answer is the one who becomes like this little child. What quality do children have that Christ would single them out? Innocence? Great smile? Quiet? While these things are good HE points out their humility.
Opposite of humility II Kings 2:23-24 - children who Elisha cursed. That is why He said little children. If the little child is not properly trained they will not follow in the right way.
God must train us to be like little children - humble
Jas 4:10 Humble yourselves in the sight of the Lord, and he shall lift you up. Phil. 2:3,5,8,14-16
1Pe 5:5 Likewise, ye younger, submit yourselves unto the elder. Yea, all of you be subject one to another, and be clothed with humility: for God resisteth the proud, and giveth grace to the humble.
1Pe 5:6 Humble yourselves therefore under the mighty hand of God, that he may exalt you in due time:
Most humbling scripture in Bible to me
Matt.12:35-36 - When is your day of judgement? Today, Tommorrow and the day after that. As Peter wrote Judgement is now upon the house of God. Thats you and me. So what must we do? Humble ourselves like unto this little child.