Do the surface melt with the heat of the body? Are they made using edible pigments? especially as the products are not made for human consumption? do they carry a warning on its box? (Something like CRAYONS CAN KILL!!!) If they don't I think that slight snacking on crayons can't bring more than a colourful tummy upset.
Not quite the same but our dog has eaten loads of wax crayons over the years and next day, it's always the rainbow-coloured poo scenario! At Xmas time, we have the sparkly poo scenario, to cheer us all up. And btw, she's never been ill on her strange diet, which has included soap and throat pastilles.