Hi there jeck2005. I think for now, stick to the 18-55 kit lens if you want the cheapest solution. If not, then I'd say 50mm f1.8 for about $180 but you'll have to manual focus so that may not be your cup of tea. If not, I think the sigma 30mm f1.4 HSM would suit you but it goes for about $700-750? One thing you should consider is what else would you be taking pictures of and then see if it is worth the investment. For taking photos of your baby, I think to make it hassle free, you should use a lens that has AF.
A few other pros of an investment into the 30mm other than the AF is that it gives you almost a 'what you see with your eyes' angle of view. So what you see with your eyes, you can more or less raise the camera and frame the shot your eyes saw. Try this out with the kit lens at around 30mm.
Also, consider if you would be taking photos in low light environments eg. christmas lights with your baby. The f1.4 aperture should give you quite a bit of speed in that area to compensate for handshakes.
But if you don't see yourself shooting in such situations, then I'd go with what chanjyj says, the kit lens should be more than sufficient. At the risk of sounding a bit warped, try imagining situations you'd be taking your baby and snap away eg. couch, living room etc. Then see if it is satisfactory to you.
And also, if you intend to take photography a little further you might want to consider using a D80 and then use the 50 f1.8 which will AF on the D80 body. Assuming you haven't bought your camera yet. All in all, test out your kit lens first.
oh btw, as to what lenses you need, I think only you would know best after shooting a few weeks/months with your kit lens.
Only when you realise that indeed the kit lens cannot satisfy what you are hoping to achieve, then start looking out for lens to serve your purpose.
For me, I MF a 50mm f1.8 on a D40X coz it gives me the speed in low light situations. of course, using a manual focus screen helps alot. I realised this after trying to shoot in low light with my kit lens.