However, there are a few things to keep in mind:
* The series spans a wide range of difficulty. The early books are definitely easier than the later ones, which can be more challenging and appropriate for third and fourth graders.
* Individual children's reading levels vary. Some children who are technically at a second-grade reading level may find the books too easy, while others may need additional support.
To be sure, it's always a good idea to check the specific book's Lexile or Guided Reading level before purchasing it. You can also ask a librarian or teacher for recommendations based on your child's individual reading ability.