A friend put down his son's 15 yo German short hair last week.
Luckily, the vet allowed his son to be with her.
Most vets will allow it if it isn't too traumatizing for the kids.
I know everyone is different about their feelings on this subject.
When we had to put down our 17 yo Bengal cat four years ago, my wife and I were there with him. I just felt that he was there for us during some really difficult times so we needed to be with him when it was his time.
It was one of the saddest days of my life because he really was my buddy no matter what.
My wife and I are now going through the same thing with our 13y/o "pup".
She has heart failure and pulmonary edema.
Even though she takes five meds 4 times a day, we know that each day is a gift and the inevitable is around the corner.
Crap, I am tearing up as write this.