Learning Style To BlameYour child's learning style will determine whether they enjoy creative writing. If they find it difficult to write about topics such as "If I had a magic potion" or "My first dragon", they may have a non-preference in holistic information processing as well as a non-preference in high persistence.
Feed the WellYou can help your child exercise their imagination by reading them a lot of story books, thinking up beginning of stories and asking the child what happens next, showing them how a real-life experience such as a trip to the fun park could be used in a work of fiction ("The princess went on the Spine Inverter Ride and BOOM she lost her crown. Oh no, she cried, I can't go back to the palace without it. Nobody will recognise me!"), or throwing random words into a hat and pulling them out to create a story line.
Assess and AssistSometimes, though, your child's imagination will simply go on strike. There isn't much you can do, except make sure that the child is as comfortable as they can be in their working area while they're writing their homework story.
A comfortable working area, one that's optimal for your child's creative muse, is different for different people. Some children will need bright light, others a healthy snack to nibble on. Some will want to be on their bed, others at their desk.
Assess your child's Learning Style to see what helps them concentrate. If you satisfy all their environment and physical learning needs, you'll make it easier for them to handle a homework task that's outside their comfort zone.