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seven is actually a really sad, haunting song. An analysis:
I think it’s about Taylor as a child being carefree and happy, referencing her biggest fears as being scared to jump off a swing into a creek, but then witnessing her friend have much worse fears as he lives in a bad household with a hateful father.
She interprets this through kid lenses “I think your house is haunted, your dad is always mad and that must be why” = the hateful father. And she wants to save him so she says “I think you should come live with me and we can be pirates and you won’t have to cry”
Then they are grown and she asks him to remember the good times they had. “Please picture me in the trees, before I learned civility I used to scream any time I wanted,” meaning to remember her before she matured and learned the harsh rules of the world & the darkness in it.
And at the end she says she can’t recall his face anymore since it’s been years & they grew apart but she wishes him the best in life, once again revisiting her childhood wishing she could’ve helped him. “pack your dolls and a sweater, we’ll move to India forever”
And last, “passed down like folk songs, our love lasts so long” because she wants everyone to remember their story. And “folk” because folk songs have a history of being repeated over & over to generations to keep the stories and memories alive. 
Also, she sings, “Are there still beautiful things?” She asks herself that after the horrible things she sees her friend going through. And she has grown up and seen the evil and wickedness of the world, leaving her innocence and blissful ignorance behind in her childhood.
