This is my dilemma....

I'm planning on having my DS1's 5th B'day party at home.He wants to invite all his kinder class which is fine.My concern is that i have been to many parties where parents bring their other children( some have 3 or 4 other kids with them) as well.
I don't have a huge house or yard and would prefer parents to drop their child off and pick them up when the party finishes. Parents can stay if they really wish too, but I really don't want an extra 20 plus kids to feed and entertain. There will be about 30 + kids and adults already.I'm also considering hiring an entertainer, and some charge extra per head over a certain number of kids.

How can I phrase the party invitation to deter extra children turning up, or to encourage parents to drop off and pick up their child rather than hanging around?. The party will be fully supervised. Anyone faced this scenario before...All ideas/opinons will be greatly appreciated!