I found this tutorial for some cute baby hats and just had to make them. My son is still pretty little (he'll be 3 months old next week) and the hats you can buy at the store are either too small or way too big. I got the tutorial from Prudent Baby.
For this hat I used their one knot and just used a old knit t-shirt.
I also made one that has two knots on the top. But it isn't knit fabric and won't fit over my babies head. :) So make sure that you use knit fabrics. ;) I really like how they turned out and can't wait to make some more.
The great thing about these hats is that I just used old shirts and only had to sew one side. All together I think they took about 5 minutes.
Happy St. Patrick's Day!