the book opens with the mc finding and describing (not graphically) a dead dog. the dog didn't die naturally, it was killed, but you don't see that happening. it is a driving point in the book and mentioned fairly often
The R-word never appears specifically, but early in the book Christopher narrates that him and his classmates are often called derogatory terms, and he lists a few.
Christopher talks about stranger danger briefly, describing it as "when a strange man offers you sweets or a ride in his car because he wants to do sex with you", he is not worried about this and it doesn't happen but it is worth n9ting imo
Nothing too graphic in the novel or the play, but it's mentioned that some of Christopher's classmates at school are epileptic. He occasionally brings this up in the narration.
Christopher almost does on the train (both the play and the novel), and it's mentioned a few other times throughout the novel as having happened in the past.
the main character/narrator has autism and is often verbally berated for it (more specifically for not understanding things, "throwing a fit", etc), sometimes even physically
Less so in the play, but in the novel it's clear that Christopher's extremely avoidant eating habits have caused some health issues in the past. He often forgets to eat, won't eat foods that are touching, and avoids anything yellow or brown.
Protagonist is a stereotype of autistic people. He’s also ableist to higher support children which is implied to be an autistic trait but they’re completely separate and this conflation is harmful.