I agree in that these books can be entertaining for adults and children. However, after my daughter brought one home and she read it me, I was a little horrified.
As college educated parents, regularly encouraging proper grammar, I found this book encouraging of poor grammar. Also, my child's school (as do we) discourages the use of words such as "stupid" and "dumb." My daughter actually stopped reading when those words came up and said she didn't want to say them.
The particular Junie B. Jones book she brought home presented Junie spying and humiliating her teacher. There did not appear to be any consequence or repercussion of her actions.
My daughter was instructed not to bring home any more Junie B. Jones books.