TNG "When the Bough Breaks". TNG didn't know quite what it was since it was going back and forth between Roddenberry's indulgences (aka "Justice"/"Planet of the Baby Oil") and being a thoroughly family-friendly-if-not-kid-leaning show ("When the Bough Breaks","Symbiosis"). This eppy is a bit oversimplified and narrow in scope (the Aldeans wanted only 7 kids on the ship?!), but enjoyable nonetheless. And there are some deeper issues that are pushed aside in favor of the then-topical ozone hole crisis. It's an understated little gem.