See for example http://www.psychologytoday.com/articles/pto-20030430-000001....
The paper is "Implicit Discrimination." Marianne Bertrand, Dolly Chugh and Sendhil Mullainathan; American Economic Review, 2005, 95(2), pp. 94-98.
if you have access. Unfortunately, I don't at this time.
The basic results are that a resume with a 'black' name versus a 'white' name (and no other difference) are far less likely to fetch callbacks. Further, there's no appreciable difference in callbacks for black candidates with increasing skills, whereas there's a drastic increase for white candidates.
There are many other studies, and then there's my own, personal experience, which I'm not about to get into.
At least people generally recognize that sexism is wrong. There is a lot less raised consciousness when it comes to ageism.
You start college early, and everyone says you're too young. And then later, ironically, you find when you hit 30 that the thinking has recently shifted when it comes to start-ups, so then you're too old.
"Update: Removed potential confusion around labor discrimination."
EDIT: apparently the source has been revised to make it clear that the point is just to look evenly at parents and non-parents; that's OK, but I'll leave the comment above in reference to the earlier version.