They can't, and that is what is going wrong with our society today.  Right now I'm a college student, I work as a substitute teacher, and I work in a gym (ok, ok, I probably wouldn't HAVE to work in the gym, but I like working there).  I make 6.50 an hour at the gym, figure 130 or so every two weeks.  Since I just started going back to school, I can only work 2 days a week as a sub, making 90 a day.  Thats 180 a week, 360 every two weeks (before taxes.... the government TAKES 25% of that... and I still don't get free healthcare or education or anything that those evil socialists over in Europe get).  I also don't ALWAYS work 2 days a week because sometimes the jobs just aren't there.  I'm 25, I live at home.  Now thats partly because I'm chicken**** and assume I couldn't make it out on my own on that paltry amount of money (without getting several roommates anyway), and partly because I'm realistic and know I couldn't make it out on my own on that paltry sum of money.  
Now, am I a ****up?  Sure, that isn't even an issue.  Fortunately, I'm not a ****up with a family, or I could guarantee you MY kids would turn out just as ****ed up as I am, and probably worse.  I think even Grunherz would understand that if someone makes less than ~$20 an hour with full benefits, they can't support a family.  Want to guess how many kids have parents (or even worse, parent) working two jobs with no benefits just to feed their kids and keep a roof over their head?