LKG orientation is a weekday morning and both parents are 'compulsory'. I have OPD

Our younger one starts LKG in June, and the school has sent a notice for a parent orientation on a Wednesday at 9.30. 'Attendance of both parents is compulsory.' My partner can go. I have outpatient clinic that morning and swapping it at short notice means someone else's patients wait. Our elder one is in his teens, so I've done school orientations before and I know roughly what gets said. Is 'compulsory' a polite word for 'strongly encouraged', or do schools really note who didn't come? Do I write to them, or just send my partner and not make a thing of it?