My situation is really similar to Steiner's. My wife had #3 the first day of winter quarter finals. We also have a 5 and 2 year old. My schedule was extremely busy but I made it through just fine. You will need to prioritize, but it is very doable.
My school offers childcare assistance for families with children, and that significantly reduced tuition for our children's childcare. Definitely also look into WIC and Medicaid - they have been lifesavers.
I think that generally speaking, some schools will be better for families than others. Some favorable qualities that I can think of off the top of my head include the availability of childcare assistance, family housing, the availability of nearby affordable daycare, school schedule where you are not in the classroom all day (mine unfortunately is classroom intensive, others are not), support group for students with families or at least school counselors who arrange get-togethers for students with families (last year there were several such parties), the ability to expand an academic year (such as stretching 2nd or 4th year over two years), availability of affordable housing nearby, ability to commute to school using public transportation or walking/bicycling, a good financial adviser who is also a student advocate and will work hard to get students the maximum amount of financial aid, and last but not least, having other students with children in your class because they are an excellent resource as well as a friendly ear who will understand what you are going through as a parent-student much more so than your younger, single classmates.
I'm sure that there are many other things that I could think of to add to the list, but success in medical school with children, esp newborns, can be pretty school/environment dependent, i.e. it would have been a really difficult year for me physically and mentally if I had to commute by car or if housing was so expensive that we had to cut corners in other areas of our life just to get by.
It can be tough but also very rewarding.
Good luck and congratulations on your wife's pregnancy.