It's possible that there were isolated instances of parental concern or school librarian decisions regarding specific books in the series, but they haven't gained notoriety or widespread attention like other challenged books.
It's important to remember that:
* Challenging books is a complex and subjective issue. What one person finds objectionable, another may not.
* The criteria for challenging books vary greatly. Some challenges are based on religious objections, while others are based on concerns about content, language, or sexual themes.
* Not all challenges are successful. Many challenged books remain available in libraries and schools.
If you have specific concerns about the "Alvin" books or any other children's literature, it's best to consult with your local librarian or educator for more information.