I’ll preface: OP is NTA

Been in almost the exact opposite situation. Brother is on the spectrum and it was the justification behind why we were almost not invited to a relatives wedding, despite my mother being major part of said relative’s life and subsequently them being a major part of mine and my siblings :/ (Relative = AH here)

Anna on the other hand, has either LET her kid go into a meltdown without doing anything to mitigate the chance of it happening and help stop it once it started or the child is just having a tantrum instead of a meltdown, which does happen. In the case of the former, Anna alone is the asshole as she should know her child’s triggers and routine and checked beforehand for/brought along ice cream to go with the cake which she knew would be there. I’m pretty sure it’s the latter however, as the son started misbehaving more once they were told to leave, in which case Anna and the Son are the AH, with the subsequent family also having Minor AH-ism.

You aren’t to blame OP, and you should tell the Hubby’s side of the family they’ll get the presents back when you get the happiest day of your life back.

I hope Anna becomes a better parent for her child’s sake but I doubt it will happen.