You would imagine that children came into the world knowing how to get on with others, how to be very fair to all, how to be a good friend to all, how to stand firm and not just follow the strongest.
They have to learn it. They are very egocentric to start with. They have to learn that the universe doesn't revolve around them. It comes easier to some than others. Some have good role models in the home, they are taught to take turns, they can't always have their own way, they have to respect other's personal space, to empathise with others etc etc . They learn how to deal with those who grab their toys, won't give a turn to anyone else etc.
Like anything- they learn by their mistakes. They get things wrong.
They haven't achieved it all by 4 years old.
It is much easier for the child who has the kind and loving family, parents who listen to them, help them bear disappointments, and sets boundaries.
It is much more difficult if the child comes from a chaotic or dysfunctional family, or where the parents want to be a friend rather than parent, or where they have delayed development, or where they are on the AS spectrum..
I know many adults who haven't achieved it! And yet it appears to be expected that the under 11yr old should have got it. MN can be very bullying.
While I can quite follow that you wouldn't want a child that yours has problems with at his party, and there is no need to have them, I think that if at all possible you can try and find a solution that is kinder. A smaller party is the east way.
( if they are only little and can't remember names you just have to ask the teacher or TA- they will know who they are most friendly with.)
There appear to be people on here who were bullied and have a huge anger inside them that they have never dealt with. Instead of dealing with it they are channelling into anger against the child that is bullying their child. They don't give 'two hoots' about the other child- they want that child to know that they 'are a horrible child and that is what happens to horrible children' .
Meanwhile bullying is complex and some intelligent children can bully without getting noticed- they still get invited to the parties. Forcing one child, by effort of your will, to hit another child is worse than the one doing the hitting- especially if they get away with it. Or it is IMO.