I was in the same boat for my eldest last year, and again this year for my youngest.
I went for a Voodoo Maji (WSF of the Hoodoo) for #1 (at 20% off). It was the only decent compromise with a 1x, XS frame and air forks that I could find.
It’s hefty though.
There’s a Diamond Back that is 1x, but is over £600 I think.
I don’t get the economics of 1x vs triple. With no front mech to fit, less metal on the chain ring and no shifter, can a triple really be cheaper?
Anyway, take a look at a Hoodoo / Maji. If you find a better 1x please post back as I do need something for my youngest fairly soon.
I’ll be looking out for that Nucleus coming into stock in the meantime.