The old nylon invisible thread did stretch and come loose. It also wasn't very bleach or even hot water friendly for baby quilts. The only issue I could think of with polyester invisible thread is just that it is so hard to see any stitches which would pull out and wrap around little fingers or toes. The one I just used on a wall hanging is 90 weight, very very fine. It is the very devil to see! There are other polyester threads in 90-100 weight that have color that might be a better choice.