I was surprised to find out children with lead poising may not ever show symptoms. It is so easy for a child to get lead poising. See this article on Lead Base paint. https://www.hud.gov/program_offices/healthy_homes/healthyhomes/lead.
If you are buying a home prior 1978 make sure you receive a copy of the lead base brochure. http://www.oregon.gov/ohcs/hd/hrs/cfcreserv/home_lbpaintbrochure.pdf