321. And the name of him who sat on it was Death, and Hell followed with him. This symbolizes the extinction of spiritual life and thus damnation.

Death here symbolizes spiritual death, which is the extinction of spiritual life. And Hell symbolizes damnation, which results from that death.

Everyone from creation and so from birth has, indeed, spiritual life, but that life is extinguished when the person denies God, the sanctity of the Word, and eternal life. He extinguishes it in his will, but it remains in his intellect, or rather, in his ability to understand. This is what distinguishes the human being from animals.

Since death symbolizes the extinction of spiritual life, and hell the resulting damnation, therefore death and hell are mentioned together in several places, as in the following:

From the hand of hell I will redeem them; I will free them from death. O death, I will be your plague! O hell, I will be your destruction! (Hosea 13:14)

The cords of death surrounded me... The cords of hell surrounded me; the snares of death came to meet me. (Psalms 18:4-5, cf. 116:3)

Like sheep they are set for hell; death shall be their shepherd...; hell shall be their home. But God will redeem my soul from the hand of hell... (Psalms 49:14-15)

I have the keys of hell and death. (Revelation 1:18)

A child is a young boy or girl in the care of parents, older than a suckling or an infant, but not yet an adolescent. "Children" are sometimes used as a name for a large group of descendants of one person, such as the Children of Israel, or even all human beings as the Children of Men. A child represents innocence and charity, where innocence is the willingness to be led, and charity is love. This is why Jesus blessed them and suggested that we all become like children in order to enter heaven.