It seems like there are so many times when I read EllenS's posts and just want to say, yes, I totally agree.
I think that, in general, letting "kids be kids" sets young people up for a life in which they don't know how to work hard, where they don't work hard in college because it's just an extension of childhood, where they go out into the real world and have trouble adjusting to working hard all day because it's a completely new experience. I think that teaching kids that they are valuable and important, that they can do real things that benefit themselves and other people, might help with some of the problems our society has with "perpetual childhood" and adults who act like children. In fact, our childhood of play, with a few chores, is so completely different from basically how most children have lived throughout all of human history (except perhaps from the upper classes and nobility, who lived lives of leisure even as adults anyway). It's not cruel to expect a child to do real work. Now, if the adults really are sitting around sipping margaritas while the kids are working all the time, it's certainly going to create resentment. But if the family as a whole works together, I think that's a good, not a bad, thing.
That said, that's how I want to raise *my* kids, but you have the right to raise yours differently. Or, at least, you should. So I think that it's a decision for the parents to make. I do think that grandparents should generally talk to the parents about what they're planning to do with the grandkids if it's any different from how the parents might expect. For instance, I would expect that if my parents watched my kids for a week, they'd probably take them bike riding, to the park, to a farm, to the mall, to various fast food playgrounds, to visit local relatives, to swim in their pool, etc. Because these are typical things that they do with the kids. I'd also expect them to have the kids unload or load the dishwasher, set the table, clean up after themselves, maybe even help with laundry. So I wouldn't expect my parents to specifically inform me that they were planning to have the kids do these things.
However, I *would* expect my parents to inform/ask me if they were going to take the kids to an amusement park, to visit relatives, or go camping. I'd expect to know if they were going to have the kids take a history class, or spend the time there painting the house or rewiring the electrical system (although since my kids are 6, 4, 3, and almost 1, I'd be a bit shocked if they *were* going to do anything like that, but let's assume my kids are older or something). Mostly because I think that parents have the right to determine what their kids will do and how they will spend their time. Permission is implicitly given for things that parents know their kids usually do at a grandparents' house. But for things that a parent might not expect, permission should be explicit. Going to play wiffle ball in the backyard? Fine. Going to sign my kid up for a week-long t-ball camp? I'd like to know. Etc.
So, to summarize, I think that the main issue here is not whether it's right or wrong to expect a child or teen to work while at a grandparents' house, but if it isn't something that has generally been expected of the child, or that the parent is likely to expect, then I think it should be made explicit and permission should be given *before* the event.