I would go with a square 60, just so that it is square and can be used any way they want. A very simple one is just fine for most people. DO you know if it is a girl or boy? You can do a check and solid checker board pattern. That will whip up really really fast. I would also make a ruffle on the edge if it is a girl with maybe a lace ruffle also.
I got one in a purple gingham with a ruffle and a lace ruffle and I absolutely loved it. My DD uses it still and I made one similar for my son. hope this helps.