From my experience people people normally say thanks for letting me know etc and great. I'm a bit miffed as this is the same mum who ds invited to his party the other week only for them to reply and say yes and not turn up no explaination. A week later they've invited ds to their party I've text to say ds would love to come sorry your dd didn't make ds party hope all ok and I've heard nothing back. I just feel bloody awkward. I do not know the mum either.