Lead has been the source of many issues over hundreds/thousands of years. The Romans used to drink from lead cups, the colonists in the US used to use lead for tools and more, and lead is still used today in many industrial settings.
But why is lead paint in particular so bad? Lead is a neurotoxin, and is especially harmful to children. The EPA mentions children under 6 years of age as being the most susceptible, because that is when the majority of brain development happens in humans.
Lead paint is found in older homes. But it is a particularly problematic issue because of lead dust. A child does not need to put a paint chip in their mouth to be affected. Lead dust is released into the air when lead-painted doors and windows are opened and closed, or when work is being done on the home.
This dust is under 4 microns – so it is invisible to the human eye. Be sure to protect your family – especially young children. Consult the EPA lead paint manual and have your home properly tested.