Fossils. What is better than fossils in your backyard. Who doesn't remember digging for fossils in the driveway?
My granddaughter, who is just starting chapter books, likes to read these books and/or have them read along to her. Why?
Ivy and Bean are friends. Good friends. Being a friend and having a friend is an important thing, and appeals to my reader.
Ivy and Bean have very different personalities. It's not a good girl/bad girl deal. Kids who generally behave well but sometimes mess up are also appealing, and identifiable.
Most Ivy and Bean adventures arise from goofy stuff that pops into their heads, (ghosts, finding fossils, and so on). Well, my girl can't actually do magic either, but she understands pretending really hard.
It's not a lot of fancy princess stuff. That was fine, but we're moving away from that. (But there is a lot of dressing-up from the dress-up box; and that's fine.)
The parents are loving and supportive. That is a great comfort, and I simply do not understand kids' light entertainment, (as opposed to "problem"), books that feature idiot, distant, or absent parents.
Everything is fueled by their imagination, which, apart from building reading skills, seems like it should be the point of these types of books.
So, dive in anywhere, the books don't have to be read in order, and just have a nice reading experience.