Together, various passages gradually draw together a fuller picture:
1At that time the disciples came to Jesus and asked, “Who, then, is the greatest in the kingdom of heaven?”
2 He called a little child to him, and placed the child among them.
3 And he said: “Truly I tell you, unless you change and become like little children, you will never enter the kingdom of heaven.
4 Therefore, whoever takes the lowly position of this child is the greatest in the kingdom of heaven.
5 And whoever welcomes one such child in my name welcomes me."
(Mt 18)
13Then people brought little children to Jesus for him to place his hands on them and pray for them. But the disciples rebuked them.
14 Jesus said, “Let the little children come to me, and do not hinder them, for the kingdom of heaven belongs to such as these.”
15 When he had placed his hands on them, he went on from there.
(Mt 19)
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though it may not be needed, we can gain yet more broader context:
5 “See, I will send the prophet Elijah to you before that great and dreadful day of the Lord comes.
6 He will turn the hearts of the parents to their children, and the hearts of the children to their parents; or else I will come and strike the land with total destruction.”
(Malachi 4)
13But the angel said to him: “Do not be afraid, Zechariah; your prayer has been heard. Your wife Elizabeth will bear you a son, and you are to call him John.
14He will be a joy and delight to you, and many will rejoice because of his birth,
15for he will be great in the sight of the Lord. He is never to take wine or other fermented drink, and he will be filled with the Holy Spirit even before he is born.
16He will bring back many of the people of Israel to the Lord their God.
17And he will go on before the Lord, in the spirit and power of Elijah, to turn the hearts of the parents to their children and the disobedient to the wisdom of the righteous—to make ready a people prepared for the Lord.”
(Luke 1)
Why this special emphasis on loving our children, in particular? Consider: it might have plausibly been a different wording that would seem ok: "...to turn the hearts of the people to their neighbors" ('love your neighbor') for instance. But it was not that, but instead it was "to turn the hearts of the parents to their children".
He says "the kingdom of heaven belongs to such as these", and we can sense right off I think that there is something about children that is the right way, the way we should be, and which is acceptable to God, as He wants us to be, as confirmed further in Matthew 18.
But, for myself, I'm already content with the straightforward wording of the Matthew 19 quote by itself. It's conclusive to me.