I'd like to introduce dd to some science fiction (something more sci-fi than fantasy). The main problem is some of the adult themes. She's 7 - but I will be reading it to her so could help it if it gets a bit complicated. But she follows the page so I can't actually skip bits.
I have the Anne McCaffrey dragon books - but they are really fantasy rather than SF. I don't feel any of my own proper SF is sufficiently child-friendly (although she has enjoyed my ancient Star Trek annuals).
I remember reading some Tripod books when I was younger. Just googled it and apparently they are by John Christopher. I really liked these.
I also think Crystal Singer/Killashandra by Anne McCaffrey were possibly a bit more sci fi than the Pern books. (I am visiting the library tomorrow and I am going to get Crystal Singer and Killashandra because I loved them!)
As stargirl1701 said there are children's Star Wars novels.
As well as the Young Jedi Knights (about Jacen and Jaina Solo) there are Junior Jedi Knights (about Anakin Solo), Galaxy of Fear (set after episode IV), Jedi Apprentice (about the young Obi Wan), Last of the Jedi and five or six Boba Fett stories. If she likes Star Wars they could keep her going for a while.