Please stop being mean to low level characters in leveling dungeons

My brother is 9. I got him a gaming pc for us to play together. He's always been interested in the game cause I've (29) have been playing it all of his life and he'd watch me playing it asking me about my cool dragons I'm riding. He made a hunter cause he's new and has been having a blast leveling. He asked to do a dungeon cause he got to 15 and unlocked it and I couldn't because I was in the middle of a raid. He got into 3 different groups and everyone was rude to him because he didn't know what he was doing and he got kicked. I could understand it if it's m+ and someone bricks your key, I'd leave too but in a low level leveling dungeon. Please as a community can we have some more understanding and make the game more enjoyable for new people? Think back to how you were when you first started wow and now imagine yourself in those shoes. You wouldn't want to get made fun of or kicked out of a group.Just be nice to each other please. Sincerely, a guardian/brother of a 9 year old new wow player.Edit: the people questioning my parenting, I'm still very new to this. I've had my brother for only 2 years now after our fathers untimely death and I'm still learning everyday on how to be a better parent/guardian/brother to him. I don't believe 9 years old is too young to play this game but you have made good arguments that I shouldn't let him do dungeons alone. He's in my very friendly guild and they've been interacting with him..in the future, I'll just let him run with myself or other guildies.Edit 2: thank you to the parents out there giving me nice words about including him into my hobby. I started doubting myself cause of the comments but the positive ones are helping me out. Thanks :)