Here's something easy for you to make for your kiddos.
Collect empty film canisters. Purchase fun foam hearts with adhesive
on the back. Take the adhesive off one of the hearts and stick it to the middle of the film canister. Select another heart the same size, put the heart directly on top of the previously adhered heart. You will Have two hearts stuck on top of each other that are stuck to the film
canister. Now have the children push the heart into the ink pad.
Then let the children stamp paper to make their own valentines.
You can easily make these with other fun foam shapes. Understand that you can only do this with shapes that don't have a mirror image.