I like to make my baby quilts a little larger and call them "play" quilts (which I hope encourages them to "use" the quilt). I want the parents to have a little room to sit on part of the quilt to play with the child as he/she grows and for the child to have room for toys to play on the quilt. I prefer not to have to piece the back so if I want it wider, I just add border(s). I think about parent and toddler (as child grows) sitting under the quilt as the parent reads to the child too. I guess what I'm saying, like others have said, is make what pleases you size wise.