One of the events on Totsy is for Book Bundles. There are several different ones to choose from. You might want to consider these for traveling, rainy day buckets or just summer reading times.
Dinosaur Train Bundle for $4.99.
Mr Putter and Tabby Bundle for $7.99. My kids love this series! They make for a great chapter book.
Curious George Bundle for $7.99.
Mad Libs Bundle for $5.99. Remember doing these as a kid?!
If you are looking for a great series for younger kids, I recommend checking your library for the Puppy Mudge and Henry & Mudge series. They are really cute books.