My family makes all the baby blankets/quilts into an about 45" square. That way, you can wrap the little one no matter what corner you get them on. Also they are large enough last awhile. My DS just outgrew his for night-time use and he is 4.5!
If the fabric has some sort of pattern on it, it will mute it out a bit. If you do this pattern I HIGHLY recommend strip piecing, it will save your sanity. Quilting in the right color of thread might tone it down also.