Adjustable skates vs used skates in incremental sizing?

[Skating_Bob]

Greetings All!

My kids (5 & 6) have expressed interest in inline speed skating - Assuming they get to the point where their current inlines are hampering their progression - would it be a better ideal to get two pairs of adjustable skates (Atom Pro Kids or maybe Luigino Mini Challenge) vs 4-5 pairs of used boots of incremental sizes?

I would imagine for the smaller kid, it'll probably be better to transition from rec inlines with a smaller wheel (80-84mm) instead of the stock 100mm wheels that the Atom & Luigino come with...if doing that it may be better to start with a shorter frame (something made of 90mm or less)?

Finding boots in sizes 10j, 11j, 12j, & 13j seem pretty rare? Even more rare small frames in that fit them (150-165mm, under 10")? The Atom Pro kids start at 11j (adjusts from 11j - 1)

Looking forward to your inputs!

Thanks!