I think it's really important to say things in a nice way as Lulu says, mostly because you are not only helping your child, you are showing your child that rules apply to all and also you are teaching them problem solving techniques as well as social etiquette and how to deal with confrontation.

The worst is when you see other parents turn into banshees, that does nothing but teach children how to be bullies themselves.

See I dunno about that Audax, I think it teaches our children passive aggression and judgement iykwim?