This Life Hack was sent out from Mrs. Stein when Liam was in Kindergarten, and I haven't forgotten it.

Trace your child's foot on a piece of styrofoam (or your's...I do this too!). Cut it out and put it in the boot - under an insole if there is one.

Here's the orginial post:

http://www.cooldad.ca/en/cold-little-feet-of-sadness/