I agree."When I was the same age as my sister was when she had her first kid, I was interviewing for postdocs. One professor told me that if I were planning to have kids during the postdoc, I was just wasting his time and shouldn't bother taking the position. "
This is the kind of cr** you should not put up with. You should remind any such creep that he needs to make his decision based on the stated qualifications or else you will report him to the relevant authorities and then sue him for gender discrimiantion, but first, to paraphrase how one of my male friends put it in a similar situation, you will kick him in the b***s.
However, it is worth keeping in mind that sometimes there IS a "rational" reason for this kind of behaviour (which does not excuse it). Most research projects run for about 3 years (at least here in Europe), and if you are lucky enough to get enough funding to hire a post-doc the last thing you want is for that post-doc to be absent for one of those years; especially if the idea is that the post-doc in question is going to be working with one of more PhD students and perhaps be responsible for a crucial part of the project (e.g. fabrication of samples).
The only long term solution to this is to make funding academia more flexible. This is already happening in some places (e.g. Sweden), mainly because men starts going on longer paternity leave (most men of my age or younger will spend at least a couple of months at home) which means that it doesn't really matter if you hire a man or a woman (although I've also heard of people who try to avoid hiring people who might want to have kids in the near future, i.e. by only hiring people who are single).