I need an old steam pump sound, and the best I can find (http://www.freesound.org/people/3bagbrew/sounds/73415/) has occasional child-sounding voices in the background. I'm a bit of a noob to Audition; is there an easy way to remove/reduce these voices?
I'd say short answer, no. You have a few options, which aren't very good.
You can cut the clearest sections and use only that. I heard a few parts without kids screaming. But then it might be choppy. You'd have to crossfade the pieces and hope they sync up well.
You could also buy software. I don't have any that could do this. But people talk about izotope rx all the time. I believe that might help, A LITTLE.
If your audio is stereo you can do what all good scareokee machines do (pun intended). In Adobe Audition simply open your audio clip as a waveform and select Effects Rack (usually left panel)>Stereo Imagery>Central Channel Extractor>Select "Vocal Remove" under preset and click apply. Voila stereo voices be gone.