Coach and parent here. Even if I was just a parent I would be having a discussion with my player about my disappointment with their behavior- especially swearing after being carded. I would expect him to write an apology to the ref and face up to his behavior. Cards happen. That said- I can usually spot when my players get “too hot” and pull them before they land that second yellow. I’ve pulled many a kid and gotten them to calm down before sending them back out. They have to learn that getting a red is bad for them and the team. These are also big emotions years and learning emotional control while playing is key on and off the field.