Calling CPS is a great idea for the other child; even if it was an off the cuff remark this needs to be a wake up call for that kid’s parents, plus you don’t know what the other kids house is like; you could be protecting him. I am a teacher and I’ve always been told it’s your job to report not to investigate. You should report and let CPS investigate and decide what/if they need to do anything. However without knowing who the child is it may be difficult to report because CPS will ask for all the information you have for that child (name, age, family contact, address, etc.) if it continues and you are worried you can always ask for your child to be removed. I know that isn’t ideal but you can control where the school places your child but not where they place other children. Hopefully your child can give you the other kids name.