I call this T's old man sweater - the combination of heavy cables and the shawl collar makes a cardigan that looks like it's made for a grandpa, and that just makes it extra charming on a little boy.
The pattern is Trellis, from Knitty 2005, and I used Debbie Bliss Cashmerino. It's a great yarn for baby things because as a microfiber/merino/cashmere blend it's soft, squishy and machine washable - without being made of squeaky acrylic. It also knits up fast, and I haven't noticed any pilling yet.
The pattern was great, too. It was easy to follow, and had enough going on to make it interesting, but it wasn't too crazy I couldn't knit while watching tv, listening to a book or while in company. I also managed to get it finished in only a couple of months (a normal person could probably knock one of these out in weeks). I made a 12-mo size, but there's not tons of room to grow and he's only 7 months old, so keep that in mind.
The red buttons came from my grandmother's button stash, and they're absolutely my favorite part of the sweater, aside from the kid wearing it, of course!