Welcome to Fishlore!
Some mollies will eat their own fry, which is why some people do the maternity tank. You let the mom drop the fry and then pull her out so she doesn't make them into dinner.
http://www.fishlore.com/NitrogenCycle.htm
Read this article. It's a bit long, but it's got really important information regarding tank health.
The short of it is that, with fish in an uncycled tank, I would suggest doing daily partial water changes (with an understocked tank like that, 25% a day would probably be good). Test your water every day, just before the water change. Once you get to the point that you've got no ammonia, no nitrites, and a nitrate reading, your tank has cycled, and you can switch to weekly water changes.