I found a book series that Brandon (who is almost 5) really enjoys, called Henry and Mudge—about a young boy, Henry, and his canine companion, Mudge, an English Mastiff.
This one, called Henry and Mudge and the Best Day of All, is Brandon's new favorite. (Is it any wonder why, since his 5th birthday is on the horizon?)
There are 28 books in the Henry and Mudge series, which Cynthia Rylant has written over a 20 year period starting in 1987.
In doing a little digging, it appears that this book series might be commonly found in 2nd or 3rd grade curriculums—but for now, my son thoroughly enjoys having them read to him... over and over again! ☺