In the old days, this was done by an artist freehand while looking at a subject using small, sharp scissors. I once watched a woman in her 90s cut portrait silhouettes of my son from black paper and glue it to a background back in the 70s. Amazing.

If I was to do one now, I'd take a snapshot of a child's side view and make my own by tracing from the photo. You can easily enlarge it on a copy machine and cut out around it for a template.

I remember...way back when I was a kid...standing in front of a wall with a piece of paper taped to it. Then a light was pointed at me and someone drew a silhouette out of my shadow.
Salijo

I did this, but on paper for Mothers Day for my kids this year.I took pics of the profiles of my 3 grands, and printed them out the size I wanted......cut them out, traced them onto the paper I wanted, cut it out again.I even went as far as on one of my grandsons, used decorative scissors to cut the hair sticking out at the back of the head, to make it look a little more realistic.....lol....
You could do the same thing with fabric.....that is how it used to be done before we had so many creative tools to do it now

Oh!!! Thanks so much you guys! I'm gonna give it a whirl!