i can't see the picture either.
I presume they are LBMs [little brown mushrooms] generally they are safe for children to play on, unless they are babies and put stuff in their months. Some little brown mushrooms are deadly poisonous but have to be injested (brown, with brown gills), some are hallucengenic (bruise purple), some are contain nerve poisons (white funnel shaped) but mostly they are harmless, and help break down nutrients for plants to use, and are just part of ecosystem. They can't harm children during normal play.