50 Cent -- I Bought My 2-Year-Old a Mercedes Benz

50 Cent and his son Sire now have matching rides ... after 50 surprised him on his 2nd birthday with a miniature motorized Mercedes ML450 SUV. Whatever happened to Big Wheels?

According to our sources, 50 surprised his boy in Los Angeles this weekend with the sweet little car ... which 50 picked out himself.

We're told the two spent the weekend together eating lots of birthday cake and 50 footed the bill for his big party on Monday.

Go shorty, it's your birthday!