I don’t read a lot of children’s books (well, my youngest has finished high school), so I’m definitely going to focus my answer on Young Adult titles. However, I do have one picture book to recommend:
Marty’s Nut-free Party and Emily Eases her Wheezes by Katrina Roe: picture books which explain allergies and asthma in an age-appropriate and fun way.
Young Adult
Invisible, Invincible, and Being Jazmine by Cecily Paterson: a compelling trilogy about a deaf teenager that addresses both the difficulties of living as a hearing-impaired person in a hearing world, but also at the challenge all teenagers have with fitting in with their peers and finding their place.
This Quiet Sky by Joanne Bischof: a Christian historical novel about a teenage boy suffering from a fatal illness.
Perfect Mercy, Amazing Grace, Love, Mercy (the Beautiful Lives series) by Elaine Fraser: a series set in an Australian high school, with each book dealing with a different issue high schoolers face—peer pressure, body image, social justice, and sexual orientation.
The Boy in the Hoodie by Catriona McKeown: a term’s worth of detentions, an unlikely friendship, and some lessons about life.