Finishing the baby's I-Spy quilt

I made the 64 block, stitched the rows together then finished the top but Jenn and I decided to make the quilt a bit bigger. It's 48" square...4 foot. She thinks 5 ft square will be a more useful size into the future. I agree...for playing on, picnics, cuddles. So now the question becomes, do we add more blocks and make it 10 blocks x 10...or 100 total? Or do I make it a border. Any opinions?