Can I stop my ex-son-in-law playing dangerous games with my grandchildren?

[NanaGary]

My daughter's ex-husband has just posted a video online of my 13-year-old granddaughter creating a flamethrower by firing an aerosol over a lighter held in her other hand. When I remonstrated with him he told me to mind my own business. It is my own business if my own grandchild (and her brother) are being endangered by this idiot, isn't it?

Your daughter might be able to do something. Not sure you can.

You mean the children's father? If so YABU. You are not a parent.

I'd report that to school tbh. That's horrific behaviour

I'd report that to social services, and show them the film. He is not a fit parent - he's endangering the life of his dc.

He's a ginormous idiot.

You've tried to get him to see reason, he won't.

If your DD can't put a stop to it then the next stop needs to be SS.

Your daughter needs to save these videos/photos and call him out on his behaviour.

It is incredibly stupid and dangerous but the fact he’s upload that is embarrassing for him.

I can imagine lots of his followers will see him as a bad parent now.

Thanks to all for your comments. I remembered right away that grandparents don't have any rights over grandchildren (though I do have the additional annoyance of childishly sneering comments on the family WhatsApp group from my 50-year-old-going-on-14 idiot of an ex-son-in-law). And you are all perfectly right about the stupidity of his behaviour. My daughter wearily continues to battle with it all - luckily it is only rarely that he does dangerously stupid things. I can only say to those of you at an earlier stage of this kind of saga: do whatever you can to stop your kids committing to relationships with unstable/immature/reckless people. And when you fail at this, you have my sympathy - I've been there! Let's leave it at that.