I am also considering this frame from BXT but with carbon fork. I do not think that my daughter needs a suspension fork for her style of riding and it adds weight too. But it seems that nobody produces 24er thru axle carbon fork, they have just standard QR version. The only one I have seen is on WOOM off5. Has somebody of you came across any 24er fork for thru axle?

About the length of cranks and fitting in general I found lot of inspiration on hupcc.com. They have completely different approach and prefer 28" wheels even for small frame sizes. So another option for a kid's bike (and an alternative to HUP) could be getting Chinese TARMAC SL8 clone or DOGMA F clone in size 44 (43). HUP suggest 44 size for 138+ cm body height. And the geometry is almost the same. Starting with flat handlebar and 26er wheels (if they fit) would be better for us. Standard open mould frames usually start with size 49 and it is too big.