In the Bible, things that are lower down, or under, physically, generally represent things that are lower or more external spiritually. In some cases, the lower things have been separated and put away to protect the good, but in others, it can mean that a less exalted idea or good desire is supporting a more exalted one.

(Reference: Arcana Coelestia 4564 [1-2], 8610, 9656)

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.