Can you repaint? Keeping the paint in good condition (intact) and not allowing baby to chew on windowsills, etc. is about all you can do. If you sand, contain the dust, wear a lead-safe mask, wash your clothes, etc. Also, if you can wipe your shoes when you come in the house, or better yet, have a shoe-free home that is a great way to not bring in lead from outside where it chips from the exterior of buildings and gets into the soil. That is how we address is at our house.
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What is your state legislation regarding landlord responsibilities and lead paint?
In the meantime I would vacuum religiously, paint over surfaces like trim and windowsills, and put bite protectors (like the ones that go on cribs) on edges that a toddler would chew on (like the edges of windowsills)
In addition to the other great suggestions you got, I would also make sure you are drinking filtered water. Lead is most likely in your pipes, too. And even though your baby is a bit young for this, just don't let him play in any dirt around your property. We live in Boston where there is lead everywhere since everything is so old. Our DD's lead levels were always very low, though, just by following some of these steps.