In our last house, the downstairs double-hung single-pane windows had these stops that allowed them to be opened slightly, enough for some air but not enough for anyone to climb in. There's a picture of this item here:
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The brass track is screwed onto the front of the wood frame around the upper pane, and wraps around towards the glass. Depending on where the sliding stop is, the lower part of the window will either slide up all the way, or hit the stop after opening only a few inches.
Now in our current house, we have double-hung double-pane windows: the depth from the surface of the wood to the glass pane is only about 1/4", while these stops require about 3/4" to 1" (that's the length of part that wraps around towards the glass). I am told that many/most double-pane windows are like this. So the window stop won't fit on the window.
Is there a solution for such windows?