Maybe if young folks could afford housing they'd have kids...there's a thought.
This is often a commonly blamed reason, but I think the data at this point pretty strongly suggests that the more affluent a country is the less kids they have. You look at some of the most third world places in the world without strong economic security, yet somehow they manage to have babies at a higher rate than Western countries do.
Even within Western countries income is negatively correlated with fertility - those most able to afford kids are having the least number of kids.