yes they are, also also standard ds games will fit.
there is a slot underneath the console for gameboy advance games and also standard gameboy and gameboy color games to be played.
However, be aware that there is NOT a gameboy advance slot on the DSi (normal or super-sized) as Wilkesneil suggests. You cannot play Gameboy Advance or Gameboy Color games on a DSi
You can on an old fashion DS however, which is probably what Wilkesneil is thinking of.