dumb_blonde:

They are the ones raising a brat, not the kids fault.

You don't know that they are raising a brat. I think you are off base. Lots of pre-schoolers bite and it's a real problem for many parents.

Telling someone not to hit your kid does not mean you are raising a brat. I think the BIL handled it well by acknowledging that it was a reflex on the part of the LW. Furthermore, the BIL had to say something to the LW about hitting--otherwise the nephew might think that hitting is OK. To avoid "raising a brat"--guess what--you gotta teach kids that it's not OK to hit, regardless of what someone else does to you.