Simplify the following text for a Grade 6 native English-speaking person.
Original: With Vettel moving to Red Bull Racing SÃ bastien Buemi and SÃ bastien Bourdais led the team 's assault in the 2009 World Championship .
Simplified: With Vettel moving to Red Bull Racing SÃ bastien Buemi and SÃ bastien Bourdais were the Toro Rosso drivers for .