A good way to introduce Runes is to get a good book and some clay. Tell the child what a shape represents and the sound it makes. Then ask the child’s opinion on the shape. This information goes into a Book of Shadows.
You can use many different things for runes. When hiking, search for small, flat stones.
You can also give children clay and let them make the rune coins, either by the shape itself, or by inscribing the shape onto a lump of clay. I would encourage making rather large runestones (about two inches in diameter) so that there is room for decorating. You can also use dough, cardboard, paper mache and stones. Draw the Runes symbols with laundry markers, acrylic, and food coloring, or carve them with toothpicks.
A truly fun activity is to make sets of cookie runes for Yule gifts and ornaments. Just use your standard cookie recipe and paint or pipe the Rune on with thin royal icing. Collect interesting tins at garage sales and swap meets. You can make decorative bags out of hems cut off skirts.
One result of this activity is that your child will have a second alphabet that can come in very handy for secret messages.
I think that a personally made set of Runes has much more meaning and magick than anything you can buy.