I set up a golf tee activity for Tara when she was younger (http://homelearningfrombirth.blogspot.com.au/2010/07/golf-tees-and-marbles.html) and this one is similar but i excluded the marbles as Mason is only 20 months and our activity shelves are left for use during the day without supervision but i thought we would revisit it as Hammering is a favourite with the boys!
In a plastic container i flattened out some plasticine to form a thick layer. It is best to use plasticine as it wont dry out if left on a shelf. In anther container i left some golf tees and a hammer along side.
I took one tee and pressed it into the plasticine then picked up the hammer and tapped the tee until it moved deeper into the plasticine. Then repeated.