The Qick Guide to successful children's parties
The Quick version of The Complete Children's Party Survival Guide

Invitations

Only invite as many children as you can comfortably accommodate.
 
 
Avoid inviting known troublemakers.
The optimum time for a successful children's party is two hours.
 
     
 
Avoid adding additional time at the beginning and end of the party for taking coats off, putting them on, giving out party bags, etc.
     
Make a separate list of the party time and the names and number of guests invited.
 

For more detailed information on the above points see Chapter 3 of:
Birthday Clown with cake
IntroThe Complete Children's Party Survival GuideInvitations