Reading a poem, quote, joke or short powerful piece can be a great writing unblocker. Read out loud together, then ask your child to 'quickly take ten minutes and write whatever this makes you think about'.
Some good website sources for 'unblockers' are
Some kids will write a reaction to the piece, like what they thought about it or how they liked it. That is ok, but I ask them to 'make something new from it'. Take the 'Underwear Poem' for example:
As soon as Fred gets out of bed
His underwear goes on his head.
His mother laughs “Don’t put it there,
A head’s no place for underwear!”
But near his ears, above his brains,
Is where Fred’s underwear remains.
At night when Fred goes back to bed,
He deftly plucks it off his head
His mother switches off the light
And softly croons,”Good night! Good night!”
And then, for reasons no one knows
Fred’s underwear goes on his toes.
If the child reacts to the poem and writes something along the lines of 'that was funny', suggest streaming ideas like 'underwear on head..underwear that is red...under hair that is red...'. and encourage them to come up with their own ideas. (as my daughter says - 'blood that is read, under your head...') To encourage originality, for this exercise I would suggest not to correct structure, though it doesn't hurt to pick some spelling words for a later test.
Got this idea from a writing prompts book at Jonathan's Educational Supplies, I don't remember the title of the book!Example: