Learn English – Are there any similar phrases that are popular in the US to express “penny dropped”

In play is the correct term here, as it refers to items that are currently in use in some process (and does not pertain to children in any specific way). "Once your hand is beaten, the cards are thrown out and are no longer in play".

I would also suggest that the issues "at hand" would flow off the tongue even better than "in play". At play, I believe is really pushing the boundaries of what that phrase means.

You can look on the black side, take a grim (or black, or dim) view of things and consider that the outlook is bleak and that the {prospect is / prospects are} grim or things aren't looking good.