Such sweet die cut stickers with gummed adhesive on the back were all the rage until the 1970s when self-stick adhesive stickers became the norm.
Gummed adhesive needs to be water activated before it will stick. This usually meant that one would lick the sticker. However, we suggest that you use a dampened sponge or cloth to activate it. Because these are old, we think you might even need to add a bit of white glue or other adhesive to make these really stick.
The little die cut measures 1-1/2 inch wide by just under 1 inch high.