I had big plans to do this with the boys and post it here but party plans are getting in the way so instead I'll just share and hopefully show our posts later.
The short version is gather flowers/leaves (on a nature walk?) spread them out on textured paper (like watercolor paper) and cover with a paper towel.
And you have a fun print!
Go to the Build/Make/Craft/Bake blog to see the full tutorial. So fun!