Ok I found a few patterns, but I realized that they can all look scary if you've never knit a cardigan before! Usually when I find a pattern that looks scary to me, I just start at the beginning and go line by line, asking questions when I need to. Line by line is less scary than looking at the whole thing. And the good thing about knitting is that unlike other crafts, you can start over and you're not losing anything (except time

).
I think the easiest one I could find is this one:
Felix's cardigan. You will need both circular needles and double pointed needles, but on the plus side, there are no seams to sew afterwards (I hate seaming). I don't know if you've ever used circulars before, but they're easy, just like straight needles. In fact, you can use them as straight needles too. I always use circulars (and double pointed). I can't remember the last time I've used straight needles.
This one also looks pretty easy, but I think it looks girly so you may want to wait until you have your little one to make it. That being said, I've seen that kind of cardi on boys too, so it all depends on your tastes.
5 hour baby sweater. I made this one and it took me more than 5 hours to make, but it was pretty quick. The first picture on the page is ugly though! Scroll down and you'll see a much better version.
This one is very cute and doesn't look too complicated. You'll have to download the PDF pattern if you want to make it.
This one is a kimono but it's super cute and it uses bulky yarn so it'll go quick.
Let me know if you try one and if you need help!