I'm writing a story where some children (age 5 to 16) are abducted by aliens and now live on an alien planet. The atmosphere is similar enough to Earth's that the children don't need any special suits or breathing equipment, but I want it to be different enough so there are some noticeable effects (not necessarily deadly or detrimental). I don't have any particular atmosphere in mind and I don't really need to know the exact composition or pressure of the atmosphere since the story is told in first person perspective of a child.
What are some potential short and long term effects of growing up with an alien atmosphere? Would someone be shorter or taller? More susceptible to bone breaks? Elongated lifespan? Cognitive issues? Increase endurance?
I know that higher levels of Argon will lower your voice and I read the High-Altitude adaptation wikipedia article.