The Fourth King: The Story of the Other Wise Man, by Ted Sieger, Candlewick, 2006. Preschool to Elementary.
There are a few modern versions of this classic Henry Van Dyke tale. I chose this one because I liked the whimsical drawings.
The story tells us of another wise man beyond the well-known three. Every time he tries to catch up with the three wise men, he would encounter a situation where he needs to help a person or people. Because he stops to help, he arrives at the stable too late. Joseph has already taken his family and fled to Egypt to escape Herod. But the fourth wise man didn't really miss the Christ Child -- He was present in every person that was helped, and in one case, literally, although the fourth wise man did not know it.
The illustrations are whimsical, which keeps this tale from feeling too heavy. The whimsical illustrations also make this book very appealing to young listeners.