It's not scaremongering - these are actual, real projections. They've been produced because long-term planning is necessary. What's more, they're considered an understatement by most people who work in the actual industries affected.
But I'm going to try a different approach.
I don't know you mummy. You write as though you are already suffering from the government's ill-advised, misguided, ideologically-driven austerity programme. I'll assume that's who you are.
So, suppose you've found it tricky to manage over the last few years. You;ve found it increasingly difficult to access the things we need to live - health services would be a good example but we might include education cuts and their impact there as well. And we can assume that, economically, things are tight.
If someone came up to you in the street and said: "Put an 'X' here on this piece of paper and I will make sure that health care provision is seriously reduced, in fact, I will probably look into closing your local hospital, and free treatment for expensive conditions (cancer, maybe?) will be removed. I'll throw in decreased funding for education (that may work out to be very interesting, with those at the very bottom getting a very basic education, with extremely large class sizes) and reduced council services," would you sign that 'X'?
No. You wouldn't. Because you'd be deranged.
That, effectively, is what you have done, though.
The Referendum never, ever promised an end to austerity or re-distribution of income, or re-investment. It was purely and simply about opting out of a very large trade (and power) bloc, which conferred large economic advantages (and some social and political ones) on the UK.
Having destroyed a large part of the UK's income stream, there is going to be less income in the UK.
Moreover, the income that remains will be very unfairly shared out - it is going to rest in a smaller number of pockets, in a smaller number of locations, and it will be shared less.
Lastly, my strong suspicion is that if the right wing media can get a sizeable fraction of the UK population to vote against their interests to the extent of voting for a calamity like Brexit, there is a real possibility that the next General Election will not see a Nordic-style soft-socialist government in power. Which leaves us facing the calamity of Brexit under a government that is not very interested in sharing diminished resources equitably.
I genuinely don't understand where your sanguine indifference about the effects of a 10% cut to GDP (albeit over 15 years), job losses, loss of rights on real people comes from. I honestly think it has to be a psychological defence because, actually, you do know what you have voted for, you do know that this is going to make your children's lives harder, and you have trouble facing up to that.