[Anatedhrai]

Anyone interested in writing for children's and YA markets should certainly read as many current examples of it as they can - but that goes without saying.

Once you get to the older end of YA, 13 or 14 plus say, there is very little difference in content between those and adult novels. Melvin Burgess's novels (some of which are SF are fantasy) go as far as you probably need to go with regards to sexual content. Violence and gore? Horror has been a bigger market in YA than it has for adults for many years. A challenging read? Try Alan Garner's Red Shift - it's a far more demanding (though rewarding) novel than many published for adults.

The main definition of a YA seems to be: a central character in his or her teens, and themes relevant to that age group (such as coming of age).

For a writer, other advantages include the ability to switch genres if you wish - the YA or teenage shelf in any bookshop will have SF, fantasy, horror, historical fiction and contemporary realism next to each other, and the readers don't object. (Do we get narrower-minded in our reading tastes as we get older?) There's also no obligation to produce 100,000 words plus as there is for adult SF/F. If your story is best told between 40,000 and 60,000 words, then that is not a commercial drawback. (Having said that, there are plenty of YAs over 100,000 words too.)