I am in a similar situation - double med student household and we too are thinking of having a child. I have spoken to some residents who told me as hard as it seems to do during medical school - it is much harder to do during residency. So I think you are right to keep your current plan and not give up on your dream or family heritage.
I worry a lot about the finances too. We are lucky to not have loans but would likely need to take one out for childcare. However I am have been looking into frugal living and way to earn money on the side. I even started blogging about this -
http://budgetandbargain.blogspot.com/Will it mean I don't have to take a loan? Probably not. But it might reduce the amount significantly. I live in an expensive area so frugal living tips are great for me as well.