Theophylact of Ohrid

After what He had said, our Lord teaches us a lesson of humility by His own example; He does not turn away the little children who are brought to Him, but graciously receives them. The wise men of the Gentiles therefore who seek for wisdom in a mystery, which is the kingdom of God, and will not receive this without the evidence of logical proof, are rightly shut out from this kingdom.

Catena Aurea by Aquinas ↗

Augustine of Hippo

To whom are they brought to be touched, but to the Saviour? And as being the Saviour they are presented to Him to be saved, who came to save that which was lost. But with regard to these innocents, when were they lost? The Apostle says, By one man sin entered into the world. (Rom. 5:12.) Let then the little children come as the sick to a physician, the lost to their Redeemer.

Catena Aurea by Aquinas ↗

Ambrose of Milan

It may be thought strange by some that the disciples wished to prevent the little children from coming to our Lord, as it is said, when they saw it, they rebuked them. But we must understand in this either a mystery, or the effect of their love to Him. For they did it not from envy or harsh feeling towards the children, but they manifested a holy zeal in their Lord's service, that he might not be pressed by the crowds. Our own interest must be given up where an injury is threatened to God. …

Catena Aurea by Aquinas ↗

Bede

They were bringing children to him that he might touch them; and when the disciples saw it, they rebuked them. And this lesson, full of the teaching of humility, shows that the innocent and simple can reach the grace of the Lord. The disciples rebuked those who were bringing them, not because they did not want the children to be blessed by the Savior's hand and voice, but because, not yet having complete faith, they thought he would be exhausted by the importunity of those presenting the children, like a human.

On the Gospel of Luke ↗