At my place, the killer conversation goes something like this:
“You aren’t doing anything, are you?” (From the offspring.)
“Other than writing the ending of my WIP and uploading new info onto the website and reviewing two novels and getting ready for a dental appointment? Nope, not a thing.”
“Oh, that’s all right then. You aren’t too busy. I need a favor…”
Scrub the rest of that afternoon. Could I say “No”? Certainly. Would I feel guilty. Undoubtedly. But I do whatever was asked of me, in between all the other things, because Kids know which buttons to push.