Yes, it definitely can be done, it just takes some adjustments. I have one child and many of my classmates have children too. You have to be willing to compromise in a few things and so does your spouse (and I am making a big assuption that you have a spouse - it can be done as a single mother too, from what I understand from some second year students at my school, although I imagine it is much harder).
For instance,I am not very active in school clubs because, the moment classes are through for the day, I run home. It came down to a choice between spending time in club activities and with my family and the clubs lost...
I am also not too concerned about my grades, as long as I pass the class and learn something out of it. I figured that the extra points would mean extra time away from my spouse and child and they didn't seem worth it to me. Like I said, you have to be willing to make some compromises. Unless you have a spouse who can spend 90% of his/her time with your child, you may have to let go of the ambition of being at the top of your med school class and settle for a comfy middle of the pack position.
In general, I think that the fathers in the class are better at spending more time on school stuff than the moms. It is probably part of the different demands that small children put on moms and dads, and the way moms also view their role in the family.I think in our society, as a rule, fathers spend a lot less time with their children, so there is no difference between a father who holds a demanding full time job and one who goes to med school.At least, that has been the impression I got from my classmates. You need to be married to an exceptional man, otherwise, one who doesn't mind taking care of the house AND kids.
Particularly during the first few months of school, I felt I was severely "short changing" my son. Everytime he wanted me to do something with him, I was locked up in my room studying. Later I learned to pace myself and how much I needed to study, so my life has some more balance now.
We made the situation harder for ourselves because neither of us believed in putting our son in daycare at an early age. He is just turning 3 and we have decided that now it is a good time for him to be with other kids, so he will be in daycare the next school year and we may have more time to be a couple too.
It is much harder than being single and childless but many people have done it AND kept their families intact in the process.