Sometimes, it pays to just get silly with stories. One place to start is with items around the house.
Choose random item, something you use every day, and write a story about an alternative use for that item.
For example, everyone knows you drink water out of a glass. But what if the glass is a hotel for ants, or a place for a rare flower to grow, or a glass that only works when you drink upside down, or something else entirely.
What happens when someone tries to use the glass in the usual way? How did your main character discover that the glass doesn’t work the usual way?
Choose a commonly used item, imagine an alternative way to use it, and then write a story. If your child is struggling to come up with an idea, encourage them to draw a picture of the object and what it could be used for. Sometimes drawing a picture can be helpful to unlock the imagination.
Encourage your child to be silly and to use their imaginations to create a fantastical story about the everyday objects around your home. You never know what they may come up with.