Re-sizing issues. Pull up a chair and put the kettle on, where are the biscuits?

I was intending to knit two jackets at the same time. So here you see completed the back of #1, although from this picture you can't actually see the detail of the jacket. Its Moss stitch at the top and stocking stitch at the bottom, with the cable ribbing.

I am in the process of knitting #2 and have come to the conclusion that I think I'll have to frog and re-start, *big sigh*. After knitting #1, I thought it looked rather large for the stated 6-12 months size (even though its dead on the stated measurements) and being as its for newborns (especially a twin) this would look ridiculously big. My thoughts were confirmed by Terri, thank you.

Only now, I've got to do the math for re-sizing.