Lead makes yellow and red paints have a wonderfully bright colour.
Many children’s toys had lead paint because of course the kids liked the brighter colours.
Kids also love to chew on toys… and the lead paint even tastes sweet. It was always a recipe for disaster.
Lead is definitely used in lots of old paint, but I seem to recall that this one specifically was mercury-based as mercury can induce schizophrenia and hallucinations, whereas lead’s neurological effects are in the “makes you dull and slow” camp.
Also, lead was mostly used in the 1900’s, IIRC. Before that they used even nastier stuff like mercury, arsenic ( I think arsenic in the paint was the cause of death for Napoleon Bonaparte) and chromium.
But then I’m not an MD or a historian; just a chemist trying to recall all of this from bits and pieces I’ve read over the years, so I might be way off base with some of the specifics.