Climbing higher is 2.3 grade (More Busy Times is 2.2)
New friends is 3.1 grade
I think you could skip Climbing Higher (2.3 grade level)
I picked up almost the entire set used ($2/book) so I just looked through them real quick 🙂 New Friends are bit longer of chapters, but the books look pretty similar in ability to read (it was a quick glance, not indepth)