Parents I need your help! Does threatening children to throw their toys away make them clean up?

I'm babysitting my two younger cousins tonight and my older cousin (who is their mom) told me if they they refuse or won't listen to me then threaten them to throw their toys away and it will get them to keep their things and I gotta be a but "mean" to get them to learn.
I'm not TOO nice but respectful. My younger cousins are 8 and 4.