Lee in Richmond

I made this Magic 16-disappearing-patch or some such name lap quilt for a child. I used a high loft poly batting that was given to me, knowing it would probably be too thick to quilt on my DSM, and backed it with a poly/cotton sheet.

My questions: Should I tie it with 3 strands of embroidery floss, or yarn? Is a square knot the way to go? Dab glue on the knots? Should I tie it at the intersections (tough with seams meeting there) or in the middle of some of the patches? The largest finished square size is 3-1/2". I think this poly batt can probably go 5-6"... What do you think?

Thanks for any guidance you can give.