As I recall, Junie B has a bad attitude toward authority, and she uses "naughty" language. Some parents consider her a bad influence on their kids.
I ran into a few at our school's book fairs who wouldn't let their kids read them. (Or Captain Underpants, because they don't want to encourage toilet humour. Or the Magic Treehouse because it isn't 100% historically accurate. Or, or, or... Every book, no matter how benign, was disliked by
some parent. "There are no girl characters in Winnie the Pooh!")
Also, I'm curious as to the definition of "banned and challenged". "Banned" I'm guessing means it was removed from a library shelf. "Challenged" on the other hand...? Is that just someone bringing it up at a school board meeting and saying, "I don't think this book should be in the school library!" And everyone else going, "You're crazy, dude, it's staying."?
(Caveat: I've never sat in on a school board meeting, so what follows is pure speculation on my part, loosely based on another educational organization I was part of the executive for.)
Personally, I see a big difference between the two. I would expect a school board to give due consideration to every parent's concerns, even if they're ridiculous. And, having listened, they can then say, "Yes, we hear you. And we regret to inform you that we will not be acting on your recommendations. Moving onto the next item on our agenda... Ah, Mr. Brown, you're concerned that sonnets are making your son gay?"
Banned is something to be concerned about. Challenged? I think we should all have the right to challenge anything we please, no matter how silly.