We had 10 playdates last year, 5 for DS1 and 5 for DS2. All the children invited here, went well, played nicely, tea eaten then returned home.
Once at their house for drop off the parents all said, 'we must have DS1 / DS2 over, will definitely arrange a date, would be lovely to have them etc'
But none of them did, out of 10 different children / parents, not one invite back.
Which is fine but just don't say you will invite them back infront of the child. Just say thank you for having X, glad they had a good time, bye.