At this point in the book the children are starting to descend into savagery.
Roger’s cruelty to the littluns, is an important early step in the group’s decline. Yet, Roger still feels constrained by “parents and school and policemen and the law”—the figures and institutions that enforce society’s moral code. But as they continue to build their society these “moral codes” are breaking down, but they are still there.
This is evident when Roger throws stones at Henry.
He’s throwing stones at him to show Henry his dominance over him, but Roger is intentionally missing, because of those moral codes that he was taught.
I hope that helps.