i read through only half of the thread, then showed the photo to dd, 4.5, and told her this is what some kids did, while their mama slept in.
"oh," she said. "poor children. i bet they were hungry. i bet they wanted their cereal for breakfast. they spilled some."
so i wonder if their motivation has been discussed? has the OP asked them? how did this 'fun' get started? were they trying to feed themselves and made an accidental mess and then kept on going. maybe out of fun / sensory experiences, maybe out of frustration... could be both.
when i had a flu i napped when DD and DS played together. they made a mess. (mind you, not that big, but i have huge bags of flour and cereal in the lower cabinets, and i guess this is just a matter of time
) so i know where the OP is coming from, napping and being too tired to get up. but honestly i can't imagine getting angry at this. frustrated and overwhelmed, yes. but angry?