The issue with lead paint is the children. The window keeps getting opened or closed and the paint wears off. Then the small kiddies come by and look out the window, getting any accumulated dust on their hands. Then off to the snack shack cookie jar ...and they consume the dust.
Because of education and cleanup , folks have been aware of kids and the paint. But better safe than sorry, children with lead poisoning are still happening.
Clean it up or change the windows is my suggestion. Painting with a sealer is a band-aid and false sense of fixing it.
Hope all turns out well.