When your kid asks, "Mom, can you please make me [something]..." you generally say YES!
My son asked me to make a microwaveable heating pad for his pregnant wife to help with her back pain and to use when she is in labor. As if I would say no.
I made such a pad several years ago, so I had all the stuff. Mine is on the right. I filled my pad with cherry pits (I kid you not. You can find them here.) The only slightly tricky part was finding the right fabric. I loved this print (on the left, above.)
To use: Microwave the bag for two to three minutes. Keep the bag DRY. It will be hot, but will stay warm about an hour.
These are also good for heating up your bed in the winter, or for keeping buns warm (seriously!)