Geez, I don't know how old you are, but there's no reason to get annoyed by the younger generation, whether you're in Seniors or Masters division.
If it's their first time playing, even if they've read the rulebook, they might still struggle with understanding the game. It's just a phase, and eventually they'll understand the rules. I'm sure even you had your questions about game mechanics when you first started playing; if you didn't, you may want to check if you're actually a human.
There's no reason to get annoyed. If you show that you're annoyed with them, they might actually take it the wrong way and leave, and that's very harmful to the game. So please, just show me that you're more mature than them and be patient with them. Everyone starts off as a noob.
As for bragging, give the kids a break. They're only 10-11 years old, maybe younger.
It's wrong if I start bragging about how I "PWNed everybody at States", or how I "demolished an entire BR and went undefeated". That is bragging, and I know better than to do that. Little kids, on the other hand, don't know any better. They're probably just really excited about their accomplishment, and so they want to tell everybody about it; they want attention, basically. If you have a problem with their bragging, just tell them how you feel. Let them know that bragging isn't cool, and that you realize they did great but they need to stop rubbing it in. Kids understand older people, and I'm pretty sure they will listen if you take the time to talk to them.