Here's how we know:
* Character Designs: The character designs in Sonic Advance 1 and 2 are more closely aligned with the classic Sonic games (Sonic 1, 2, 3, etc.) than the more modern designs introduced in Sonic Adventure. This is a visual clue that they happen earlier in the timeline.
* Story References: The games don't mention any of the events from Sonic Adventure, like the creation of the Chaos Emeralds or Sonic's encounter with Shadow.
* Timeline Placement: While the exact placement is debated, the Sonic Wiki places Sonic Advance 1 and 2 before Sonic Adventure, citing the game's connection to the classic Sonic timeline.
So, if you're following the chronological order of Sonic games, you should play Sonic Advance 1 and 2 before Sonic Adventure.