I think the action of these young people is heartening. It's a beginning; an awakening.
There are still many, as others have said, who think the whole subject is a joke or simply don't think it affects them in any way. The lure of Stuff in this society is what drives it and what motivates it. It's not easy for anyone to try and break free from that, least of all impressionable teenagers whose raison d'etre is to look cool with their mates and that means having all the latest Stuff (and then throw it away). Thankfully many are now realising that there is no Away and never has been.
I think I'd have the same reaction as the OP to be honest, but use this as a starting point. Any tiny inroads you can make to encourage them to question and think outside their narrow cocoon will be a step forward.
If my children were on the demonstrations I'd be completely supportive. We cannot afford to be otherwise. Yes, there are some contradictions, as Eloethan points out, but you have to start somewhere and make small changes which then grow and become big ones.
We don't fly when we go on holiday but I can't claim my carbon footprint is negligible by any means - we take the car on UK holidays and train it in Europe. We are learning all the time about ways in which we can start to make a difference but iof course we need big businesses to commit to global change. I hope it's not too late.
Parents-in-Law. What do/did you call them?
Badly Faded Red Composite Door
Elderly fellow gran has become loudly racist