I have never met silverware that could not be cleaned. i can't imagine throwing out everything in an area without some conversation about how to know whether these things were important.
I think the ladies went overboard.
And I'm sorry, Martienne, that this experience has been so painful, instead of being the big lift you expected. That's got to be doubly bad.
I do think you goofed, though. I think you should have asked your children to pick up things from the floor before the ladies came so they could focus more on cleaning, or simply to safeguard the important things from the floor. If you didn't have enough time to get ready, you could have asked for a rescheduling.
I'm sorry it was a painful learning experience. Maybe you can make it work for you if you don't focus on how wrong they were, and instead use their reaction as a tool to motivate your kids to pick up their stuff.
To get back to the etiquette--it's important for all of us tor realize that speaking up and saying, "I'd really like it if you would XYZ" is NOT a criticism. Saying to them, "Oh, I hadn't realized--are you just throwing stuff out?" would have been fine.
Or to say, "you know, let's have a strategy session here about this--I'm afraid my children's things rae going to be thrown away" is acceptable.
Sometimes when people are doing us favors, we think it's a gift and that we should just shut up and take it the way they want to give it to us. But that's not the case.
Favors can politely be declined if they create more trouble than they're worth and they absolutely can be guided.
I think your hesitancy to do that is like your hesitancy to insist that your children pick things up, etc.--you fear what others will think of you. (hey, welcome to the club!)
But I think that if you are proactive and speak up RIGHT away, while it's still in the "oh, this is a mistake, I bet you want to know" mode, and not in the "now I'm pissed off" mode.