childrens party no show/response

[tigerthecat]

How can I ensure a response to the invites i am just about to send out for my sons 5th party. last year despite sending a reminder, landline with ans machine, mobile for text and reply sheet I was unable to get responses from some parents as to whether their little smasher would come. This year I have hired a play area and there is a limit so if some kids cant/dont want to come i'd like the opportunity to invite kids who I was unable to invite the first time round. Any suggestions would be welcome :-)