I believe that the major vector indoors is dust coming from the lead paint on windows and window sills. When the wear surfaces rub against each other, a small amount of lead paint dust is created and inhaled or ingested by children.

Outdoors, the problem is the lead dust in the soil. Chickens are getting lead poisoning in urban areas:

https://now.tufts.edu/articles/backyard-chickens-and-risk-le...