For recorded times, Team Fortress 2 holds the top spot at ~1,800 hours. Civilization III and Super Smash Bros. Melee both hover at around 600 hours. And then I've got quite a few games over the 200 hour mark like Fallout New Vegas, Fallout 4, Skyrim, Tales of Symphonia, Tales of Vesperia, Warriors Orochi 3 Ultimate, Pokemon Ruby, Civilization IV, and so on.
as for when I was a Kid, my top 3 for total playtime's likely Starcraft, TIE Fighter, and Mechwarrior: 2 Mercenaries in that order. Runners up'd probably be Civilization II, Super Smash Bros., Mario Party 3, and Seven Kingdoms II: Frythian Wars