With a level of 6, I would not be worrying about the child's current health but would be checking the environment for possible sources. There has been some discussion of lowering the level of concern to 5, and I believe effects have been found at that lower level - let me check my sources though before I say that for sure. However, when I was a kid (in the late 70s), *average* lead levels were around 15, so that might give you some perspective.
I might ask the water company to test the water and/or look around for lead paint or vinyl blinds in buildings where the child plays regularly, etc., old toys of painted wood, etc. If you can reduce the exposure, so much the better. Also making sure the child's diet has plenty of calcium and iron protects against absorption of lead to some extent.