The title "Daddy" sets this up as an address to the speaker's father. Even though the word "daddy" is only used six other times in this 80-line poem, since the poem is titled "Daddy," we can guess from the start who "you" is in this poem.
It's important, though, that the poem is titled "Daddy" and not "Father," or even "Dad." "Daddy" is an affectionate name, one that a child would call her father when she's being cute, or when she wants something, like ice cream, or soda, or a pony. Also, little girls who are their fathers' pets are often referred to as "Daddy's little girl."
So it's ironic that he speaker uses the word "Daddy" to address the father that she has characterized as a Nazi, devil, and vampire. But the title isn't the only part of this poem that doesn't quite match the violent images of the speaker's father – the related "sound" of the poem is as contrast as well. It seems to us that the title "Daddy" fits with the singsong rhyme and other childish aspects of this poem, like the word "gobbledygoo" in line 42. But this playfulness, paired with the violence she describes, shows us the speaker's internal struggle between loving and hating her deceased father.