Both of my kids were raised atheist, though my oldest, growing up with his mom, attended a Unitarian Church, where atheism is common. So no harm done. Both ended up fine as adults, clearheaded, intelligent and actually educated. And I didn't have to lie to either one of them about god. I felt bad enough doing it about Santa for a few years though.
And lets see. Neither has ever been in trouble with the law. Neither abuses alcohol or uses drugs. Neither son has had to deal with awkward pregnancies (of course, the oldest, being gay, voluntarily disqualified himself from that option), and both seem to be dealing well with reality. So, from my point of view, as long as a parent is as honest about the rest of life as they are about the lack of gods, good things can come from kids.
Except for the part where they grow up so darned fast. Enjoy your four year old son, curious girl. When he hits 18 you'll find yourself swearing he grew older at the speed of light and you'll wonder where the time went.