I asked a similar question about a year ago, looking for preschool age books about nature. There were a lot of really good suggestions, and some of those will likely still be enjoyed by your 5 & 6.5 year olds.
https://permies.com/t/50433//Favorite-Preschool-Aged-Books-Nature
Another book, more of a textbook, for your older kid might be Matt Power's Permaculture Student:
https://permies.com/t/48506/books/Permaculture-Student-Matt-Powers.
As for homesteading books, fiction and historical fiction is a great way to go! (I read a lot of fantasy as a kid and it made me long for the "olden" days and want to learn various skills, like carving and embroidery and starting fires. Although medieval fantasy was a lot of fun for me, it's usually more adventure-themed, rather than homesteading themed). I would think any historical fiction or stories about the pioneers or colonials would be interesting and teach some skills, too. I've never read them, but the Little House on the Prairie books are generally really well loved. Kindergarten kids generally will listen to chapter books, especially if you read just one chapter a day and the story is below adult level (i.e. if the average 11 year old can read it by him/herself, then your younger kids will likely enjoy having it read to them).
I wish I had more book suggestions for you, but I really wasn't into reading for the short-chapter book stage of development...I didn't really start reading until 4th grade and pretty much jumped from Dr. Seuss to my mom's 200-300 page sci-fi/fantasy books...
Edit: Yikes, it took over a day for permies/my browser to let me post this, and it looks like some others already mentioned some of the books/resources in my thread. Sorry about the repetition!