https://docs.rs/bevy/0.15.3/bevy/prelude/struct.EntityWorldMut.html#method.remove_children was removed in 0.16. The release candidate migration guide https://bevyengine.org/learn/migration-guides/0-15-to-0-16/#remove-various-structs-that-implemented-command mentions a .remove_children existing on EntityCommands, but I don't see it in the docs https://docs.rs/bevy/0.16.0-rc.4/bevy/index.html?search=remove_children

https://docs.rs/bevy/0.16.0-rc.4/bevy/prelude/struct.EntityWorldMut.html#method.replace_children_with_difference seems to be the answer, but requires some additional manual work to reproduce the behavior of remove_children, this should be documented in the migration guide.