Pokemon Gold/Silver/Crystal showed off the second official region of the Pokemon games, and introduced all sorts of new mechanics that weren't present in Red/Blue/Yellow.

One of those features is Pokemon breeding. Take two compatible Pokemons, put them in the daycare, and after a while, they'll do the nasty and you'll get an egg as a reward. Which pretty much means that G/S/C made Pokemon sex canon.

And where is the daycare located in those games?

Route 34.