I think its so wonderful how moms know their kids so well! Your ds sounds a lot like mine! And your dd a lot like my dd age 8. Very creative, feeling, artistic, etc.
Here are some ideas of books my ds enjoyed at a young reader:
Billy and Blaze series
The Bears on Hemlock Mountain (Dagleish)
The Matchlock Gun
Various titles by Clyde Robert Bulla (some are more “begining” than others)
And…don’t throw tomatoes…the Nate the Great Series. I know Nate the Great is not a “Great” book, but for a brainy-boy-beginning reader they were high interest, benign mysteries, with a good amount of humor. That kind of lead to him loving the Hardy Boys…which again is not fantastic literature quality, but great for skill building. I will say though, he has transitioned into reading a wide variety of literature now, though his love for mystery and adventure has not waned. Now, his favorites are Sherlock Holmes, Father Brown Mysteries, RL Stevenson, and right now he’s reading Swiss Family Robinson!
For you dd, my daughter is enjoying the Betsy-Tacy series, Understood Betsy (one of MY favorites!), EB White collection, and her absolute favorites are the Narnia books. She’s reading them all through a second time, since she “misses” the characters when the books are done.
HTH!
Shawna