Is it ok to cry in front of your kids ?

Me and my wife were watching a live concert DVD of our band last night our son started dancing when his dad was singing his dad died a month before he was born. My wife started to cry when he did that. That was the only time he stood up and danced when he heard his dad sing. She feels kind of bad she cried in front of him. I think she probably cried because she was happy. Is it ok to cry in front of your kids ?