I don't think I can think back to then, really, Boomer....and what I would have wanted...because I know what to do now!!!
But..I suppose I would want my poor parents to have been other than anything they had it in them to be at that time.
Bless their cotton socks, the situation when I was little was one for which there is now a LOT of support available...for kids and parents. There is also a lot more understanding of how kids react to trauma and such. There was nothing then...or nothing which my parents would have had the.....I dunno...confidence, wisdom (?)...to access. My mum was all about denial and my dad had the emotional wisdom of a fence post! But they did their best.
What I would want now for a kid in relation to anxiety beyond the norm is proper help.
This means education about anxiety, its physical manifestations (I use a drawing of a kid with all the parts of the body anxiety usually affects, including the brain and therefore the thoughts), the harmlessness and evolutionary purpose of said manifestations (kids often love thinking about being cave people, and how important the flight/fight response was to escape sabre -tooth tigers and cave bears and such), stuff about how, given that now most of our fears are of things that are not dangerous, and can't be responded to by beating something up or running away, the energy stays in our body and makes us feel weird, and we hyperventilate which makes us feel REALLY weird......but those feelings are harmless.
And then the work on the kid's specific fears, using cognitive and behavioural techniques.
Of course, for Mo, his anxiety is fed by his attachment stuff, and hence his difficulties with emotional regulation and some of his likely core beliefs...but you're already working on all that!!!
I like externalising the problem (a la Michael White)...so the kid can take on worry, or fears, or the worry bug, or whatever the hell they want to call it....we can then map all the things the worry bug does to try to make them feel bad, and figure out ways to beat it at its own game......worry-wrangling and suchlike.
You can make it funny and like a game, although the feelings are horrible for the kid.....cos they have to be exposed to the fear-causing situation until the fear settles.
And some relaxation techniques....breathing ones are good, I think.
But understanding is the key.....understanding the nature of anxiety is usually enormously helpful in itself. And understanding the kid....but supporting them in not letting fear beat them.