Baby legwarmers, (c) Sarah E. White.
One of the first things I knit for my new baby was a pair of custom-sized legwarmers, which you can see here. There's not really a pattern to them, they just involved taking the measurements around her ankle, the top of her leg and the length of her leg, knitting a gauge swatch and doing a little math.
I think the results are pretty adorable, and the project is so quick and easy you won't mind that the baby you knit them for will grow out of them in no time. Mine are also made from a super wash wool, so caring for them is a snap, even with a newborn.