Here "children" is a metaphor for being spiritually immature. Alternate translation: "when we were like children" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "enslaved" is a metaphor being unable to stop one's self from doing something. This can be stated in active form. Alternate translation: "the elemental principles of the world controlled us" or "we had to obey the elemental principles of the world as if we were slaves" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-activepassive]])
Possible meanings are 1) this refers to the laws or moral principles of the world, or 2) this refers to spiritual powers, which some people thought control what happens on earth.