Hi Hanna - I know how you feel because my husband and I have moved twice to new states in the last few years. What I have learned is that if I don't stick my neck out, then we're not going to make any friends. Other people are shy, and more people appreciate the efforts I make than are turned off by them.
I don't think you should feel too cautious about inviting them. Chances are good that they just don't want to impose upon YOU. Also, being busy with the baby, they might have a difficult time finding the energy to initiate a new social relationship in the evenings, and I guess her husband probably works on weekend mornings, so brunch is probably out.
How about inviting the wife over for tea one afternoon, maybe on a Saturday? But just once - if she ignores your invitation or declines it, then consider the ball in her court and move on. I do recommend
http://www.craigslist.org as a great way to make friends. Most of my friends where I live now are people I met on Craigslist, under Activity Partners (bike riding for me) or people I've bought stuff from, sold stuff to, or bartered with. Also, I've heard that
http://www.meetin.org is good too -- several of my friends participate in meetin activities. I've met some great friends with volunteer work that I do, as well.
Good luck! And welcome to PC!