Most ABC books teach 26 letters with 26 sounds, called a letter-to-sound format. In these books you will read something like, "A is for apple." In this instance the letter sound of 'a' does not match the beginning sound of "apple." I guess they assume that somehow the minds of little children will figure this out all by themselves!
In Alphabet Harbor the names of the Harbor Friends teach the sounds of each letter. For those with one sound, like Boy B, your child repeats the same sound. For letters with two sounds, like Echo E, they say the short sound in "echo" and long sound in 'e.' This relational format makes it easy and fun for all children to acquire the 40 sounds they will need to know before they begin to read.