I don't think there have been econometric studies on people having more children. But the integration of women into the labour market has been demonstrated in econometric studies that have controlled for all kinds of other variables. The combination of available day care--which is not available enough, but still, once you get it, it's affordable—affordable day care, plus the supplements, the family allowances and supplements for people who work for low pay, make it more feasible for someone to hold a job. It has increased the participation of women in the labour market. That's been established empirically.
On March 24th, 2009. See this statement in context.