I find it extremely rude that you leave the minute your son, daughter, or student finished with whatever piece he or she is playing. Especially when you sit down toward the front of the hall and parade out the minute he or she is done. I came on time and sat there quietly for every player. Even yours son, daughter or student. It’s just the polite thing to do.
Just sayin’.
Not only is it rude, but your son/daughter is missing out on an opportunity to learn from listening to his/her peers. I was amazed when my daughter was starting out in high school and I saw this happen – I don’t recall it happening when I was a student performer (just a few years ago).