lead
Lead was used as an ingredient in oil based paints until it was finally banned in 1977. The reason that lead was used is because it made the paint faster drying, cover better, have higher durability, etc. But when it does start to flake, small curious children will attempt to taste it. And unfortunately, the lead compounds have a sweet taste which will then encourage the child to peel more flakes off and eat them. Lead poisoning can cause nerve damage, kidney damage, stunt growth, and other effects.