Probably a novel.

Max was a normal boy minding his own business when he was suddenly abducted by some emo teens from his room late one night. When he realizes some rather dangerous looking men in black suits and tasers were after him as well, he goes willingly with the teens, leaving behind a letter for his parents.

He joins a larger group of kids also kidnapped by the emo teens and together they learn about new powers that they're developing, why they all have them and that the men after them are trying to correct their mistake from years ago.

Max - The boy kidnapped from his house to join a group of others like him. Also, he can heal.

A world much like our own, except here there was a small mix up with vaccines which gave certain children powers beyond their control and people who want to eliminate the children before the powers manifest, or to capture them and use their powers for their own personal gain.

I thought of the Seniors one day first. Kids were were dressed in long dark clothing for some reason that never talked. From there, I came up with reasons why they did things. They didn't talk because they had no muscle control in their tongues, they covered their skin because it wasn't all there anymore. The story came some time later.

Max will actually leave a letter behind every time they move location, which is often, addressed to his parents.