I am starting my kids off with Python personally.
I don't know if best, but I know it well and with the repl and existence of notebooks like Jupiter (https://realpython.com/jupyter-notebook-introduction/) it gives me the tools to get started and teach quickly.
Interested to see what resources others share as I not using any right now just my own knowledge of python. I did have kids learn scratch using a book as a prequel.
I did come across this book but still have not decided if I will use it: