Humanoids often refer to their offspring as a child (plural: children). While the term generally applies to adolescents, indeed, James T. Kirk once described children as "Little ones like yourselves. They grow." (TOS: "The Apple"); the term may also be applied to adult members of a species, alternatively known as a son (male offspring) or a daughter (female offspring).
Richard Daystrom compared the M-5 multitronic unit he had designed to a child, developmentally. Dr. Leonard McCoy didn't care for the comparison but used it all the same when analyzing the scientist's mindset. (TOS: "The Ultimate Computer")
Occasionally beings have posed as a child to gain insight into Humanity's existence, strengths, and weaknesses. (TNG: "The Child", "Imaginary Friend") The children of Drayan II were individuals nearing the end of their lives, rather than beginning them. (VOY: "Innocence")
Some species did not rely on offspring as a means of continuing the species. For example, the J'naii and the Changelings were two species that reproduced in other ways. (TNG: "The Outcast"; DS9: "The Search, Part II") Prior to the intervention of the USS Enterprise on Gamma Trianguli VI, the planet's inhabitants had no need for what they described as "replacements", as they were forbidden by Vaal. (TOS: "The Apple")