If they actually did those things, it wouldn’t be slander.
If I were to guess, I’d take it as “unless the kids knew/suspected with good reason they were doing those things”, because that’s how I would feel about it at least. I would still want to talk to them about appropriate responses and make sure they knew they could trust me, but kids don’t always know how to bring up adults’ misbehavior.
If it’s just a fluke, that would feel like an ends justifying the means situation.