A.C.
If this were me, I would politely explain MY household routine and inform them that I will no longer hold dinner past a specific time, and that if they have not picked up their child by that time that she WILL be fed with the rest of the family. I would explain to the parents that I feel I'm being cruel and inconsiderate by making her watch my family eat and just as cruel and inconsiderate making my family wait in order to not feed their child, especially now that they are finding that they must come later than in the past. I then would let them know that if this arrangement doesn't work for them that I will completely understand that they may need to find someone else who's schedule is more appropriate to their needs. At no point would I ask them if any of this is OK. I would tell them it's what's going to happen and I would follow through. They will have 2 choices, deal with it or find someone else to watch their daughter.