I am a border person. I think that it is like framing a picture - it just seems to bring it altogether and finish it off beautifully.

I think just a binding of a thin black and white stripe fabric cut on the bias (or not) would be cute.

Normally I am not big on borders with this one I feel it needs one or two. Green should maybe one of them or the outer border.

No border and I'd bind it in the red.

Pretty top! yes, I'd do a border or two. My personal preference. Perhaps do a thin green, then a wider yellow. Then bind in red, or a solid blue.
Whatever colors, I'd try to keep the red and green apart so it doesn't look Christmas-y.

Doesn't really need a border, but if you decide on one, I would put a very narrow stop border in black or white, then a little wider border of your choice. That would stop the colors in the quilt from blending into the border.

Infants don't use quilts in their cribs, but toddlers do. Actually as soon as a child can roll over front to back and back to front items in the crib are OK. Most parents now wait until after the first birthday. So after all that, you could make it for a crib but a little wider and it would be a fun tummy time quilt.

First of all, that is a real cute baby quilt. I always like to frame my quilts with a narrow border which I think would look nice for your quilt possibly a red and then you could add a little wider border after that in another color of fabric that you can pull from the colors in your quilt. Whatever you choose it will be cute. Please share a picture of the finished project.

If it were mine, I'd put a pale yellow border, then bind it with the red or green.

I think a nice 2 inch or so border would look really nice in the red you used in the squares. It would really finish it off and make those red squares really pop. IMHO