I believe the poster above was mentioning more those that are below median income or certainly those closer to poverty levels. There are a lot of benefit programs that take number of dependents into account so if you income is remaining the same, then increasing the number of children you have increases the benefit amount you receive. I don't think you can draw a causal relationship between benefits provided (at least for many families) and increased children, but there are certain people that do know this and exploit it regularly (source: watching an in-law do it ATM).