Parental duty

Like childcare but for your parents: Sitting around all day with your parents who came visiting you.
If you're at uni and having to explain to them why you don't have a girlfriend, why you don't have good grades, why you don't have a part-time job.

And if you're married already you send the day helping your dad with his garden and your mom in the kitchen why avoid the question "So why don't you have kids yet?"

John: Hey Tom, you comin' out tonight for Lizzy's birthday party? We're out to a nice restaurant before the club at 8pm
Tom: Nah bro, I can't this time. Got parental duty
John: Shit! Good luck with that

Example 2:
Chris: The whole office is going to Disney on Saturday, will Marianne also be coming?
Alex: Nah, she's got parental duty. She's taking her mom grocery shopping, and then for a haircut
Chris: Sucks to be her