>I cannot find any reference to this as a reasoning for declaring genocide. 6 countries made a declaration, and all allegations centre around rampant killing of civilians. That's the main benchmark.

I haven't checked the PR statements, but the arrest warrant regarding the children includes the genocide charge[0], that's where the actual legal action centres, not around 'rampant killing'.

It's based on article 2(e) of the genocide convention: "Forcibly transferring children of the group to another group."[1]. Also, Russia is doing it publicly so it's easy to prove.

[0] https://www.theguardian.com/world/2023/mar/17/vladimir-putin...

[1] https://en.wikipedia.org/wiki/Genocide_Convention#cite_ref-C...