Laura Lee Hope 
The Bobbsey Twins at School [PDF ebook] 

Bert has been selected to help the school principal run a small museum at the school. But on opening day, the museum’s most valuable statue goes missing and the twins must help find it.
The Bobbsey’s train has a problem on the way home from the seashore and almost runs into another train that has come off the tracks. A circus train. They loose a silver cup and their cat Snoop and while walking to catch a trolley to get home they find a dog. Will they get to keep the dog? Will they get the cup and cat back? You’ll have to read and find out.