This is wrong, I got Totodile before delta ep, oshawott after delta ep, and I have not gotten sinnoh starters yetRoute 101
After completing the Delta Episode...
Choose either Chikorite, Cyndaquil or Totodile from Professor Birch.
After defeating the Elite Four twice
Choose either Turtwig, Chimchar or Piplup from Professor Birch.
After defeating the Elite Four the third time.
Choose either Snivy, Tepig or Oshawott from Professor Birch.