I know people who have had children during law school and have managed okay. But at the very least, I would recommend against having the child during 1L year.
Here is where being the mother matters. A dad could manage starting law school with a new born (though it would be challenging). Being a mother would be tough becuase,unless you have someone else in the house lactating, it is kind of a one woman show. Good luck.
I respectfully disagree with Ninja, though we are both speaking from our own experience. The people with kids in my class are all in the top 1/3. It is actually easier to focus on school for me because of my family.