Basically, I'm pretty sure that this song is saying that you can't judge a book by it's cover.
A persons height can't determine what they are like on the inside.
'You're only as tall, as your heart will let you be, and you're only as small as the world will make you seem.'
It's saying that you get to choose how tall you actually you want to be, tall meaning how big of a person you are, and that if you listen to the world comment about what you are on the outside, then you'll start to look as small as they are calling you.
Basically, I'm pretty sure that this song is saying that you can't judge a book by it's cover. A persons height can't determine what they are like on the inside. 'You're only as tall, as your heart will let you be, and you're only as small as the world will make you seem.' It's saying that you get to choose how tall you actually you want to be, tall meaning how big of a person you are, and that if you listen to the world comment about what you are on the outside, then you'll start to look as small as they are calling you.