Is it true that someone who oppresses an orphan is cursed by Scripture to also become an orphan? My kid came home saying that kids in his class were picking on a certain boy who does not have a mother, and one of his classmates said that they have to be careful as the Torah says that one who does so is cursed to become an orphan himself.
Yes, it is absolutely true that the Torah explicitly states that one who oppresses a widow or orphan and they scream out to Him in their pain than G-d will get angry and punish the perpetrators by R”L making their own wives into widows and their own children into orphans. [Accordingly, it is most important for a) people to beware of the feelings of orphans and be especially sensitive and careful around them and ask for their forgiveness if they have wronged them. B) it is likewise important for the orphan to be forgiving and not G-d forbid pray to G-d to punish the individual who harmed him, as we read each night in the bedtime Shema that we forgive every individual and asked for them not to be punished due to us.]
Sources: See Mishpatim 22:21-23; Mefarshim ibid [Rashi, Ramban, Even Ezra, Keli Yakar]