My nephew is having a major surgery, she does not want to tell him about it at all, is this a good idea? he is 10 yrs old

Bad idea: Not telling a 10 year old of a major surgery not only is not a good idea, but it will create alot of anxiety and resentment on the child's side

I'd suggest she tell: It isn't your decision; however, I would suggest that it is his body and he has a right to know what is going on. Children are more capable than we give them credit for and NOT telling is more likely to cause trust and betrayal issues as he will obviously eventually know and have to recover.