You're probably being downvoted for being wrong. In the novel, he had 5 kids, but also the entire point of Bob Cratchit is as an allegory for the working class, so criticizing him for having too many kids is hilariously in line with Ebenezer Scrooge pre-ghosts. You might as well have said that Mr. Cratchit should've let Tiny Tim die so they wouldn't be so poor for maximum irony.
Having a large number of kids was really common during that time period. Back then kids often helped around the house and on the farm; plus it was pretty common for kids to die before reaching adulthood which is another reason for the large number.
It wasn’t until around the 40s or 50s that the 1-3 kids per family became common
It's not exactly funny though. He didn't have an abnormally large family. In a society where large families are common that society should give higher wages. Scrooge was infamous unfair. Others could see it too. Bob Cratchit's problem was Scrooge. He can have all the sex he wants but your joke has Scrooge controling that part of his life too.