I'm getting a bit worried about Nathan now. I know I'm probally worrying over nothing but I'm sure the girls were doing more when they were 6 months. He seems to be quite average if not a bit advanced physicaly but mentally I'm sure hes a bit slow! He doesn't seem to respond when you call his name and just seems to be in a world of his own. I just wondered how other babies mental development was doing at 6 months?