Best. RPG system. For Kids. Ever.
As it is a free product, made so during lockdown time, just download and check it. Oh, and there is more than a handful of free scenarios too, for all kind of settings described in the paid version, but you can play with them with only the Quickstart.
Detailled : all PC has 4 skills with a dice size (from D12 to D6) and roll when attempting things. 1 or 2 is a fail, other are a pass. I played with my kids on a 3 players party, from 10 to 4 and half. The paid version (which I bought month ago) has plenty of advice on how to actually run RPGs with kids, like adventures design, not to get them too afraid when very young... The quickstart has only a summary of them, still useful.
My only wish here is it could exist in other language (mine being French), to allow kids who can actually read to do so...