The Early Learning Goal for writing is: Children use their phonic knowledge to write words in ways which match their spoken sounds. They also write some irregular common words. They write simple sentences which can be read by themselves and others.
When the children are writing their stories about the Three Little Pigs, please encourage them to hear the sounds. At this stage in their writing it is ok that they are not spelt completely accurately but phonically plausible. For example:
house - howz/hous
little - litl (they wouldn't know there is double t and a silent e)
blew - bloo
If your child is already writing phonically confidently then we would start introducing the correct spelling for high frequency words.