Not many ppl like to 寫字. So, the only thing I can think of
a/ Do not force them to write a lot. I would rather write 5 words a day than 25 words a week.
b/ At early age, don't criticize too much. Praise, Praise and Praise and explain what they have done well.
c/ When playing games, try to include hand writing, say, game of 天下太平