Lead used to be part of many household items. Pencil leads used to be composed of mostly lead. (Now they are mostly graphite.) Lead was used to connect pipes, stained glass, in paint and automobile fuel.
Unfortunately, the lead was ingested in small quantities from drinking water that flowed through those pipes, breathing air with fuel fumes and by small children who tend to taste things like paint chips and pencils. This caused lead poisoning, which causes many health problems, mental retardation and can even be deadly. Young children are especially vulnerable. So, over time lead has been removed from most of these things. However, older homes may still have lead paint on the walls, and occasionally toys are found to have lead in their paint or other materials (watch for recalls).
- Wikipedia's article on lead poisoning
- Mayo Clinic on lead poisoning