Hellobee Boards

If you think you might actually use it I’d go for the crib size.

I'd do the 36x54 crib blanket size, just because I think it would be more versatile. It's still not too big that you can't use it to tuck around them in a car seat or stroller, especially if you fold it in half. Also, folded in half it makes a great bit of padding to be able to plop them down on the floor for some tummy time wherever you are. I have a lovely thick one that a friend made me that was great for that when I was out at various mom & baby group classes.

12x12 for a little security type blanket/toy/lovey is probably good, my daughter has one about that size that she loves.