When it comes to safer backpacks for kids the main thing to avoid is PVC, but other nasty chemicals to avoid include phthalates, BPA and lead (with lead the best option is to choose lead free or lead safe).
These below have murky definitions of what is used to produce their backpacks, but these are PVC free:
-See the full list with links and read information about safety here:
+Lunch boxes—You are looking to avoid the same things: PVC, Lead and BPA
-Beatrix Lunch Boxes: http://amzn.to/2bJUmj8
-Blue Avocado: http://amzn.to/2bPMV9f
-Built NY: http://amzn.to/2bK4KHM
-Information about safety here: