I've done batiking in African villages, and they use old candle stubs,
which are of course free, and the wax can be reused indefinitely.
They also use cassava paste, made of cassava (manioc, tapioca) flour.
Sometimes you can even get the whole cassava root, which is like a two-foot
long Idaho potatoe. Just boil it, mash it, and add enough water so it's
not too sticky (about the consistency of cream of wheat). This will not be
grainy like mashed potatoes, but much smoother and glueyier. This is used
in Ghana, Ivory Coast, and Nigeria. You just dump some on the cloth (still
warm), smooth it out a bit, then use combs or other implements to cut in a
design. Dry in the sun, dye (they use either natural indigo or commercial
dyes), then flake off the dried paste. They also smoosh the cassava paste
through tin stencils (you could make plastic or paper ones)--this is done
in Nigeria. This is the technique used in Oshogbo, Nigeria, to make a very
famous kind of indigo cloth. The streets run navy blue all the time!
The wax is done with wooden or foam stamps. All this is of course done
outdoors, because it's kind of messy! I have slides and videos of these
processes being done in Ivory Coast and Ghana, & would be happy to answer
questions (but I'm not an art teacher and I don't work with kids).
Northern Kentucky University