The U.S. government subsidizes children. Some parents profit from having more children.
Not just the US. I'm Belgian with two kids. I get about €300/month (around $350 USD) in child benefits, plus some tax breaks and partial reimbursement for childcare. Before anyone thinks we're getting rich off this: we're not. 😅 I'll be the first to say those benefits aren't even close to enough to justify having kids just for the money. If that's someone's retirement plan, they're going to be very disappointed.
Ding ding ding. This is an important answer. I know 2 families like this and it’s disgusting.