You will need:
Old T-shirt or upcycled fabric
Fusible webbing (all I had on hand was the tape version)
1) Find the sleeve or side of fabric that is already folded in half. Trace half of heart with the center of the heart on the fold. Make sure it is large enough to cover your tear.
B) Cut out and trim edges.
iii) Hopefully, you will have a full sheet of fusible webbing, instead of tape to make this easier. Either way, cut it out to completely cover the wrong side of your patch.
4) If your webbing does not have a backing, then place the webbing and patch over your hole and iron on. If it does, you can iron it to the heart first and then your garment.
C) Let it cool. If you want you can embellish with some chunky whip stitches to make it more patch like or let it ride. The chalk will wash off in the laundry.
It should be flexible enough to stretch with the fabric and protect those knees a little longer. ~ OP