In reply to JeroenandTimo: folk have been bouldering in la forêt for about a hundred years, bouldering mats have been around for a lot, lot less. So yes, its perfectly possible to climb without a mat although you might want to be a bit careful about landings & spotting.
You don't say what age the boys are, but several areas have kids circuits (marked in white) which might be worth looking out for.