Well, from what I've seen in the US. Many Mexicans move to the US and live with extended families, so a typical 5room house can easily accommodate that. But the next generation of those children aren't going to want to live in extended homes. They'll want to have their own place and this has economical effects like having less children. Economics plays a huge role to if people will have children too. Afterall, we're not obligated to bare children.