Fee fi fo fum is an example of onomatopoeia?

"Fee fie fo fum!" is NOT an example of Onomatopeia. Onomatopeia is a Word that sounds like what it is trying to describe-for example, buzz.

What you are describing is called alliteration- when a series of Words starts with the same or letter or sound. For example, "She sells seashells by the seashore." This is the definition of alliteration most often used, but according to dictionary.com, there are other types.