You would assume that writing children would be an easy task - "they aren't very complex" or "everybody understands the mindset of a child" are common phrases I hear when people are writing kids. But the truth is, children are as complex as adults in many ways, and writing a child (particularly in their point of view) can be challenging and frustrating.
For one thing, children tend to have this sense of idealism: that everything should be fair, everybody is equal, that the world is a good place. A writer needs to be aware that, in a child's eyes, the world is open to them, no matter their own consequences. A child will assume that they can do as they please as they get older, and a child will assume that the world will welcome them with open arms. Writing in a way that shows this, but later foreshadows on how awfully wrong these assumptions were, is extremely important.
Another aspect to consider is language. A child will speak in simple sentences, using basic words and a dash of incorrect grammar. Children seldom talk like this: "Oh, today shall be a glorious day, for the sun is shining and the sky is clear!". It's unrealistic and it usually doesn't even co-ordinate with the character. A child will cut their sentences short or trail off on many occasions, so that's another thing to consider.
A key factor in writing children is having them be rather oblivious or unaware to the things around them. Not entirely, of course. Children tend to pick up on things but not fully understand them: for example, a child would not be aware of the demands of war, whereas an older character would be.
Children usually display their fears more openly than adults. Things that are not usually scary in the eyes of an adult could be terrifying to a child, for example, the Boogeyman. Children are usually quicker to cry, and quicker to admit their fears too.
Apparently, children believe that they can get away with lying, when in actual fact, the vast majority cannot. Whether they do this consciously or unconsciously is another matter, of course, but on the whole a child will sooner blame somebody [or something] else rather than face guilt themselves.
A child's imagination is much broader than that of an adult, usually. Pretend games, imaginary friends, etc are key elements of childhood for many people. Naturally, a child can imagine things quite clearly in their head (which can also lead to over-exaggerating). A child's mind is also more open to learning: a child would usually learn something such as a language quicker than an adult.
Children are, of course, more playful than the majority of adult. They'll usually play with anybody at a young age, but as they grow they may become more particular as they slowly start to realize the society ladder. Because children are not usually weighed down with the complications and stress that come with adulthood, they tend to be brighter and more cheerful, although this can mean that they're naive as well. Additionally, children tend to be gullible to some degree. Many will copy what they see other doing or saying, and many will assume that what they're taught or interpret for themselves is 'right'.
There are so many important aspects of children that are often over-looked by writers, and these are only a few of them. So, when you're writing kids, just think logically, and remember:Â children are as complex as adults in their own right.