I totally agree with "quiltedsunshine". The serpentine stitch is a good choice because the wavy line detracts the eye from any stitching irregularities. Works either over the seam lines or through the middles. Your choice.

First off let me thank each one for responding. I appreciate your suggestions. I have a question about if he is okay for me to tie the quilt. What do you use to tie? Do you use DMC floss all six stands ( that’s what we use in small prayer quilts, or woolly yarn such as sweaters, mittens, etc are made, or cotton crochet yarn like used in old doilies, or something else?

For tying I would use crochet yarn. It will be stronger than DMC and less bulky than yarn. Just my opinion. Good luck with this quilt

I used yarn and DMC thread - both are going strong. But just to let you know, I do put a dot of Fray Check in the middle so they don't come untied.

Pearl cotton is another option. Holds it's twist better than embroidery thread.

I would also go with tying as when it was put together, it was probably the era when you either hand quilted a quilt or tied it.

Double Knit lends itself very well to tying. And, you could just place an applique over the bad section and just leave it alone. That's what I would probably do.

It will be a labor of love for your grandson.