Mushrooms and toadstools are the fleshy fruiting bodies of some fungi. Neither term is rigorously defined, so no scientific differentiation can be made.
Some say that toadstools are poisonous and mushrooms are edible.
An agaric is the classic fungal fruiting body, characterized by an umbrella-shaped cap on a stalk. Toadstools are sometimes considered to be any fungus with this shape. The quintessential toadstool is fly agaric (Amanita muscaria), a toxic fungus with a red cap covered with white warts.
Toadstool carries a fanciful connotation and may be preferred over mushroom in children’s stories.