You've gotten some good advice here so all I want to do is reiterate this:
Lead is SERIOUS. In your food means ingestion. This can cause all sorts of BAD consequences on a young, developing brain. This is nothing to mess around with. Call the rental agency again. Their excuse sucks, to be frank. No, they don't have to rebuild your house but when there is a serious health threat, it is their job to deal with it. If necessary, call the health department and get some information through them to give to your landlords. Do not wait the 9 months until your lease is up.
Here's a quote that I found online that sums up the issue:
"Lead at low levels is a serious threat to the central nervous systems of infants and children. Lead toxicity in the blood has been found not only to impair early school performance, later grade school performance, but also to negatively affect cognitive functioning into young adulthood. According to a study published in the New England Journal of Medicine in 1990:
"The persistence toxity of lead was seen to result in signifiant and serious impairment of academic success, specifically a seven fold increase in failure to graduate from high school, lower class standing, greater absenteeism, impairment of reading skills sufficiently extensive to be labeled reading disability (indicated by scores two grades below the expected scores), and deficits in vocabulary, fine motor skills, reaction time and hand-eye coordination."
Within the human body, lead damages the nervous system, circulatory and blood forming system, reproductive system, kidneys, and gastro-intestinal tract. In adults lead poisoning can cause various symptoms, including fatigue, loss of appetite, stomach disorders, forgetfulness, headaches, insomnia, irritability, hypertension, anemia, reduced desire for sex, impotence, dizziness, and weakness in the extremities.
It is much more serious when children are exposed to lead. Since the brain has not yet completely developed, lead poisoning can cause learning disabilities, attention deficit disorders, lowered IQ, and anti-social behavior. Elevated levels of lead sustained over a period of time, can damage the central nervous system of children and adversely impact their development." (lead-info.com)
Yeah, he ate paint chips and turned out fine? Look at his behavior now. That's not what I call turning out fine.