Don't make them cutesy
If your child characters are going to be cute, they must be cute naturally through the force of their personality, not because the entire purpose of their existence is to be adorable. Forced cutsiness rarely works any better than forced humor.
Don't make them sagely wise
Don't turn your child characters into little fonts of wisdom. Its true kids have the benefit of seeing some situations a little more objectively than adults but when they start calmly and unwittingly spouting all the answers, the results often seem more clichéd and convenient than impressive or ironic.
Don't make them unintelligent
Don't confuse a child's lack of experience with lack of intelligence. Don't have your child characters offer wide-eyed "I dunnos" or stand around with a finger in their mouths and a blank expression on their faces. It's fine if they don't know what's going on, but don't forget for a minute that their brains are whirring behind the scenes, trying to figure it all out.
Write them as unique individuals
Don't ever put a "child character" into your story–anymore than you would "an American character" or "a female character." Create a fully realized individual who has a reason for existing beyond mere accessorizing.
Give them personal goals
The single ingredient that transforms someone from a static character to a dynamic character is a goal. It can be easy to forget kids have goals because when we think of goals, our adult brains tend to think of lofty things like earning a million dollars, finding true love, or saving the planet. In fact, however, kids are arguably even more defined by their goals than are adults. Kids want something every waking minute. Their entire existence is wrapped up in wanting something and figuring out how to get it.
Make them smart
They may not know as much as the adult characters do, but that doesn't mean they aren't as smart as them. Now, of course, you don't have to go out and write a bunch of little Einstein's but don't make your child characters dumb on purpose.
Don't forget they are children
Most of the pitfalls in how to write child characters have to do with making them too simplistic and childish. But don't fall into the opposite trap either: don't create child characters who are essentially adults in little bodies.
If your child characters are going to be cute, they must be cute naturally through the force of their personality, not because the entire purpose of their existence is to be adorable. Forced cutsiness rarely works any better than forced humor.
Don't make them sagely wise
Don't turn your child characters into little fonts of wisdom. Its true kids have the benefit of seeing some situations a little more objectively than adults but when they start calmly and unwittingly spouting all the answers, the results often seem more clichéd and convenient than impressive or ironic.
Don't make them unintelligent
Don't confuse a child's lack of experience with lack of intelligence. Don't have your child characters offer wide-eyed "I dunnos" or stand around with a finger in their mouths and a blank expression on their faces. It's fine if they don't know what's going on, but don't forget for a minute that their brains are whirring behind the scenes, trying to figure it all out.
Write them as unique individuals
Don't ever put a "child character" into your story–anymore than you would "an American character" or "a female character." Create a fully realized individual who has a reason for existing beyond mere accessorizing.
Give them personal goals
The single ingredient that transforms someone from a static character to a dynamic character is a goal. It can be easy to forget kids have goals because when we think of goals, our adult brains tend to think of lofty things like earning a million dollars, finding true love, or saving the planet. In fact, however, kids are arguably even more defined by their goals than are adults. Kids want something every waking minute. Their entire existence is wrapped up in wanting something and figuring out how to get it.
Make them smart
They may not know as much as the adult characters do, but that doesn't mean they aren't as smart as them. Now, of course, you don't have to go out and write a bunch of little Einstein's but don't make your child characters dumb on purpose.
Don't forget they are children
Most of the pitfalls in how to write child characters have to do with making them too simplistic and childish. But don't fall into the opposite trap either: don't create child characters who are essentially adults in little bodies.