Okay- not exactly my idea- I will give credit to mermag. My stamps look a bit less fancy- mainly because I don't have too much spare time- but they function perfectly well :-)
I cut out shapes from foam rubber (Moosgummi) and glued them to small wooden blocks.
The girls enjoyed stamping faces. I should get ink in different colours- that would be even more fun than only blue.
Of course you could stamp also other things- or make templates that the kids can copy... Or stamp big paper rolls for gift-wrapping.