This page is meant to be a comprehensive guide to writing for your audience. I will define genres and age groups as well as go into things like word count. As always, these are my opinions and some of these things may differ slightly depending on who you ask. I will continue to add more moving forward and include examples. This is a work in progress, so look for information on genres soon!
Word count-600 or under generally. A standard picture book is 16 spreads or 32 pages and they're filled with illustrations so word count is generally on the low side. Of course, non-fiction picture books are an area where word count can be much higher (and can be upwards of 1,000 words). There are always exceptions, but I'd try to stay in this range to be safe.
Age range: Infant to 7. There's a vast range of picture books from board books meant for very small children/babies with very few words all the way to more complex non-fiction. Character driven seems to be what most people are looking for these days. They are stories with a strong main character who learns a lesson, or goes on an adventure etc. but the focus remains on him/her/it. Plot driven is more focused on the action/plot and to work well has to be fairly fast paced with a twist or something exciting as it's relying on that and not the characters. Character driven stories build up character and generally have great series potential as children enjoy following that character and whatever they may do.
Do picture books have to rhyme? No! Certainly not. I feel that many writers think this to be the case, but to be honest often when editors and agents hear a book described as rhyming we think, "oh, another one?" While it can rhyme, I wouldn't necessarily use this to describe it in a query or pitch. Tell us what makes the story special. Also, make sure your rhyming actually rhymes. Try not to stretch it. Also, you need to think about the flow and how you're rhyming (couplets etc.)...so you need to know a bit about poetry to make this work. It's harder to write a rhyming picture book than many might think.
Word count-25,000-50,000 words. 50,000 is on the long side for a middle grade novel, but is acceptable depending on the subject matter. Fantasy is generally longer, so I'd say this genre would be the one that will be around the high end of the MG word count and may very well exceed 45,000 words. Of course, there are always exceptions to the rule. Cornelia Funke, J.K. Rowling...Tell the story you want to tell, just be careful that you're not trying to put too much into one story. Younger middle grade should definitely be on the shorter end of this range and can go below 25,000 words.
Age range: Generally 8-12. 13 and 14 can be MG or YA. It depends on the subject matter and themes.
Audience: Middle grade readers are young children (pre-teen) so things like sex, drugs, violence (some is ok, but I'd say steer clear of blood and gore), swearing (very minimal if any. No f-bombs) should be left out. Think of a PG movie---this is about the same audience as a MG book. Of course, if these subjects are broached in an appropriate way, some can be included. I guess this is what you'd call innuendo. You don't go into detail but can imply certain things happen. There are certainly some MG books that deal with more difficult subject matters. For romance, it's more puppy dog love for this age range and generally not as key to the plot as it might be in some YA novels. Remember: Many kids this age still think the opposite sex is gross :)
Word count- 50,000-75,000. I'd say the most common length I see for YA is right around 60,000 words. Again, like MG, fantasy will be on the high end and may exceed 75,000 words.
Age Range- 13-17. So we're talking older middle schoolers to end of high school here. While young adult is designed for this age range, many older adults are reading it too, especially those in their 20's who may not yet be connecting with adult novels. Of course, with all the trending in YA over the last several years I'd say the audience goes well into adulthood.
Audience: We're now in the PG-13 age range, so sex, drugs, swearing and violence are allowed, but be careful with over-doing it and becoming too graphic. Older YA certainly allows to have more of these areas--but again not too graphic i.e. excessive blood and gore, really specific depictions of sex and/or frequent sex scenes, 100 f-bombs etc.
What is new adult?
There seems to be a fair amount of confusion about this term. I've gotten queries for "new adult" projects that are actually more tween (between MG and YA) and on the other end "new adult" projects that are actually well into the adult range. I'd personally say new adult is meant for 18-24 year olds. We're generally dealing with characters fresh out of high school, in college or perhaps just out of college. New adult so far seems to be more romancy and trying to re-capture what 50 Shades of Grey pulled off. As it's for older readers there can be more sex...more everything really. I think with new adult there's still a bit of finding one's self here.
Word count, in sum:
This area is actually pretty important to consider. While some agents don't care as much others will reject you based on a too high or low word count. Join a critique group or have some friends read your manuscript before sending it out on submission---extra sets of eyes can often help you to take out plot lines that aren't necessary and trim pages if you're looking at a high word count. Same for too low: it can help you flesh out areas that need developing.