There is a product called "Lithosketch" I think it is a US product.
It requires several compatible items. The plate ( which appears to be
similar to offset printing plates) pens and pencils and a solutioin
for preparing the plate for inking. You need their ink too. Because
it is not cheap you may need to cut the plate up into 4 A6 sized
pieces if you are going to give each child the experience. The
results however are comparible to authentic lithography.