From the letter:
Out of all on my children, and I do mean all Tommy , Ferg and you were the worst about keeping mittens on. I would see you in Interlochen your hands red from the snow and your mittens on the snow fort, and your brothers the very same way. You would come in and we would put your hands in cool water and slowly warm them up by adding heated water. A very good tip right there. But if your mittens were interesting, you kept them on a bit longer, so please my darling make interesting mittens so perhaps your children will keep them on, and when they take them off and they will as they are yours, remember the water trick and I will be smiling watching the frustration on your face.
These are the girl mittens