No defending the housekeeping or the hotel's response to it but playing devil's advocate:
Is it possible the DND sign was left out by you or the kids in the morning and wasn't taken off until later? Or you didn't vacate the room for the day until later in the afternoon and they didn't check back for service?
My family has been guilty of this many times being lazy and on vacation and not fully getting our act together (esp at resorts) and we didn't want them barging in.
Also guilty of putting the DND sign out at 7:30am en-route to the gym and forgetting to remove it an hour later when I came back. Used to find them in the room at the stroke of 8am when I had to quickly shower and get dressed for work. The better, caring hotels would place a note under the door saying they were unable to service but call for towels and garbage removal if wanted.
The SHS response was terrible irregardless of whatever went on but I've been the victim of this several times, usually family sports weekends where we want to sleep / relax late, they want to start early and go home and conflicts bound...