Not correct, war crimes can be committed by individuals including leaders
Families of Israeli hostages file war crimes complaint against Hamas in The Hague
Families of Israeli hostages held by Hamas have taken a significant step in their pursuit of justice by filing a war crimes complaint against the terror organization at the International Criminal Court (ICC) in The Hague. This bold move, led by the Hostages and Missing Families Forum, marks a pivotal moment in the ongoing struggle to hold Hamas accountable for its brutal actions.
https://aseannow.com/topic/1319916-families-of-israeli-hostages-file-war-crimes-complaint-against-hamas-in-the-hague
The ICC can only investigate and prosecute “natural persons” who are over the age of 18. The ICC cannot investigate or prosecute governments, corporations, political parties, or rebel movements, but may investigate individuals who are members of groups.
ICC link source