The birth rate in most western countries is below 2.1, which is a negative replacement rate. That means people actually aren't having tons of children. The population is seeing a decrease in the amount of young people there are to take care of the elderly through social security. The idea that poor people and people on welfare are just cranking out kids to get more money is a myth. Some might do it, but it certainly isn't too widespread. On average, couples in the USA aren't even having enough children to replace themselves. The USA's rate is something like 1.8. Considering 14% of the USA lives in poverty, if poor people were doing that, that rate would be a bit higher.