Your interpretation of this poem's title is a sound one, and is supported by the poem's final word, "too." The poem is divided into two sections: one focusing on the speaker's daughter and her concerns about her appearance, and the second focusing on the speaker's son and his similar concerns. Although the two sections are divided, that final word, "too," unites them—it is the note on which the speaker leaves us, and it resonates in conjunction with the title. The girl's experience is, in many ways, different from the boy's: they are concerned about superficially different things, but there is a sameness in their self-criticism that is far greater than these differences. The girl's daily makeup ritual may look different to the boy's weight-lifting and jogging, but both are fundamentally the same thing, "the same song" of a teenage desire to improve what they see in the mirror, something that makes both of them "frown."