I sure don't know why this is billed 'for little girls' because my 5 year old son loves it. He loved the stories from age 3 and still loves to listen to them. I have a feeling he associates with the naughty little sister - she's a bit naughty and gets really angry sometimes, but at heart she's a nice kid.
I loved these stories when I was a child and it's great to see that they still appeal. They have a timelessness - just about being a child in a world you don't quite understand always. Not sure how much they would appeal to those very young children who appear to have been brought up on Harry Potter (at 5??) but you never know, it might give them a step back into a gentler, more appropriate place!