Fantasy/ YA person falls into alternate universe where they have to fight a war. Only kids are fighting and they have all been here for different periods of time and I don’t think they aged. Read in 2011.

[Morgan]

At the end I think they come out through a sewer and they go back to their own time period. Friend from other universe finds them but has aged. This was read to me when I was in 6th grade in 2011

[Rainbowheart]

Huge long shot, something in the Found series?

[Kris]

Morgan, can you describe this alternate universe and how it's different from the "real world"?