I don't tend to have a lot of kids in my books, though I've written my share over the years. I don't know if they just don't generally fit into my style, or if I've had too much personal experience to want to deal with them at work, too, or if I have doubts about making them real or sympathetic or authentic.
I find a lot of kids in books lack authenticity. They're props more than anything else: they come in when they're needed, then disappear again. When they disappear, man, are they gone! Not a peep, not a concern from Mom or Dad about doing their laundry, fixing their food, overseeing their homework, refereeing their fights, etc.
(I knew a woman who did this in real life. When she needed to impress people with her maternalness, she trotted out her adorably cute kids. The rest of the time, they pretty much ceased to exist in her world. Amazing.)
But authentically written kids can be a pain. I read for pleasure, not to observe some whiny brat having temper tantrums on the page. Yeah, real kids whine and have tantrums. No, it doesn't entertain me.
And so I find myself currently writing a whiny brat. She's got reasons for her behavior. Life has not been kind. But writing her character means treading a fine line for me. I want her to be realistic for the situation she's in and for people to understand and sympathize with her, but I don't want her so realistic that readers are saying, "Sheesh, get this kid off the page!"
Who would have thought that I can handle hundreds of adult characters with ease but just might be done in by a thirteen-year-old girl? :)