Research has found that children learn to spell in much the same way as they learn to talk. They begin by approximating words and move through a process which eventually leads them to use conventional spelling.
In the meantime, they need to be surrounded by meaningful language (as opposed to lists of pre determined words), immersed in reading and writing and taught spelling strategies that work for the individual.
From the very beginning, children are encouraged to try to write down words - they "have a go" and invent the spelling which may or may not approximate the word.
For instance, during the very first stages, they might use one letter to represent a whole word; later on, it might be two or three letters.
Their approximations gradually become more accurate as they become more familiar with conventional spelling and learn more about language and the visual patterns of words and letters.