The faith of children is also a recurring theme in the Bible.

Matthew 18: 2-4, for instance

^2 He called a child, whom he put among them, ^3 and said, ‘Truly I tell you, unless you change and become like children, you will never enter the kingdom of heaven. ^4 Whoever becomes humble like this child is the greatest in the kingdom of heaven.

1 Corinthians: 13 (one of the most-quoted chapters in the Bible, and a beautiful description of love even if you don't have faith) also compares the difference between childishness and adulthood to the difference between the partial understanding of the universe we have now to true understanding.

13 If I speak in the tongues of mortals and of angels, but do not have love, I am a noisy gong or a clanging cymbal. And if I have prophetic powers, and understand all mysteries and all knowledge, and if I have all faith, so as to remove mountains, but do not have love, I am nothing. If I give away all my possessions, and if I hand over my body so that I may boast,[a] but do not have love, I gain nothing.

Love is patient; love is kind; love is not envious or boastful or arrogant or rude. It does not insist on its own way; it is not irritable or resentful; 6 it does not rejoice in wrongdoing, but rejoices in the truth. It bears all things, believes all things, hopes all things, endures all things.

Love never ends. But as for prophecies, they will come to an end; as for tongues, they will cease; as for knowledge, it will come to an end. For we know only in part, and we prophesy only in part; but when the complete comes, the partial will come to an end. When I was a child, I spoke like a child, I thought like a child, I reasoned like a child; when I became an adult, I put an end to childish ways. For now we see in a mirror, dimly, but then we will see face to face. Now I know only in part; then I will know fully, even as I have been fully known.

And now faith, hope, and love abide, these three; and the greatest of these is love.

In order to see the magic of Narnia, childishness is required, because to see it as an adult is to see beyond the fantastical. In understanding, the ability to see the magic is lost.