Planning for 3rd Grade – Creative Writing Suggestions?

I am currently homeschooling an 8 year-old and I have a 2 yr old, as well. We love our CM learning. Right now we are doing handwriting/copy work, we use Pathway Readers and I spend 30 to 45 minutes per day reading aloud to him. We use AAR gently, slowly as tool for our reading. In 3rd grade I’d really like to incorporate some creative writing encouragement into our homes school day. My son really enjoys making (and illustrating) stories. Sometimes we do this together for fun. I do not want a creative writing curriculum at this point. But, are there any suggestions for story starters, or a book that one has used as a creative writing resource?? I feel like he would enjoy a story starter/creative writing fun in our day once or twice per week. And, with a two year old, I’d love to have a book/resource to use rather than creating or trying to think of something on my own. This would be more for fun, but also a good practice for organizing his creative thoughts on paper with mom. Any advice/help is appreciated.