I think it is nice the way it is.

I usually do piano key quilting on plain borders. It adds a lot of visual impact for little work.

I was thinking cornerstones, too. Rather than undoing the border, you could just applique squares in the corners.

I think red balloons would look adorable. I'm picturing a large balloon in the corner, big enough that it goes into the green strip, not just in the yellow, but that might not be what you had in mind. The balloon string could run down the side or to the middle like the little elephant is holding it.

I love the balloon idea. I've seen similar added to borders and they started at the top left and came down about half way or a little more. Then the right side started in the middle or up a bit and came down to the bottom. I also would maybe make 3 balloons 2 on one side of the string and 1 on the other. kind of like flowers growing only balloons. If you machine applique the balloons you could also machine sew the string. This a very cute quilt and doesn't need much on the border.

If you do crosshatch quilting in the yellow border it would make a big impact and is easy to do to :-)

I think it is perfect as is. The bright blocks and borders really look great on it.

Some interesting quilting shapes in the light border with a darker thread can jazz that up. It is looking really cute so far. He will love it.

Serpentine stitch would look cute ! Love the bright colors. What quilt pattern did you use?

I think it looks great.. but its your quilt. I wonder what type of binding you are going to use? that could dress the edge of the quilt up some and make a pop. (like maybe the green polk a dot fabric used in the body of the quilt??)