Fiendish children

Succubi and incubi are probably the most common tanar'ri to be produced through sexual union, given their natures. If you are intent on detailing the maturation of such fiends but want to avoid any possible moral quandaries regarding preteen succubi, as many probably would in their games, I suggest giving them a development cycle similar to the Xenomorphs from the Alien movies. Let me give you a run down:

Sexually produced succubi and incubi can be said to resemble human babies at birth, albeit ones with clawed wings, pointy teeth, and a thick covering of slime. The toothy little cherubs are able to crawl immediately upon being born, and their first action is to instinctively flee from their mother. The pain of childbirth is much greater for the tanar'ri than for any mortal race, and the succubus is likely to kill her offspring out of sheer agony. Their first order of business is to seek a small, enclosed space in which they can safely lick themselves clean of their slimy coating. Once done, the young demons are able to spread their wings and use them for unsustained bursts of flight. Their next goal is to find something weaker than themselves, usually an isolate mane or dretch that had gotten separated from its horde. They carefully stalk their prey, making sure that it is truly alone, and then strike, preferring to attack from above with a high-pitched shriek. Flapping around the victim's head like a swollen bat, they tear mercilessly at the eyes until their victim succumbs to its wounds. They then burrow into the flesh, which swells shut around them. The body grows to almost double its size before taking on a dry, leathery texture. Within an hour, the dry husk splits apart to reveal a fully adult succubus or incubus, complete with sex drive. Their first equipment is usually made from the leather of that very first kill, although it holds no sentimental value and is discarded immediately upon their discovering something better.

Awesome, Iavas. I like it.