According to the young-earth perspective, when were races created? From Genesis, God created Adam and Eve. How come we have so many races on earth if we came from the same parent? Is it because people changed physically by adapting to various climates? Or races were made when different languages were introduced in Genesis 11 vs 6-8? How can I explain the human race diversity given the literal Biblical account?
Based on the wording of your question, I assume you want a literalist/young earth creationist perspective. This isn't the only perspective in Christianity. Plenty believe in evolution, or one form of Old Earth Creationism or another. The last portion of this answer, on particular, will likely be jumped on by the OEC and Evolutionist crowds, as it's specifically a literalist/young earth creationist view.



Technically, from many Creationists point of view (Kent Hovind, Ken Ham, Henry Morris, me) there is only one "race" . The "human" race.  The idea of dividing up God's people into an artificial grouping based on superficial differences is wrong, anti-Biblical, and offensive in and of itself. 

From ICR.Org


  "Race" is strictly an evolutionary concept used by (some) to rationalize
  their white racism. But from the beginning it was not so! "God that
  made the world and all things therein; . . . hath made of one blood
  all nations of men for to dwell on all the face of the earth" (Acts
  17:24,26). "Have we not all one father? hath not one God created us?
  why do we deal treacherously every man against his brother?" (Malachi
  2:10).


The thinking described above is known as "scientific racism", and is generally denounced today, for good reason.

An interesting observation, taken from http://www.bible-truth.org/race.htm


  The question we must first answer is: "Are there races of men?" The
  difficulty of classifying man into races has been shown. Perhaps a
  better term would be "varieties" of man. Even evolutionary science
  concludes that all existing varieties of man are members of the same
  species.2   Inter-racial marriages are common and children are
  produced with no biological difficulties. Prominent anthropologist,
  Ruth Benedict in her book, "Race: Science and Politics" stated the
  peoples of the earth are a single family and have a common origin.3
  
  Once supposed biological differences, such as dissimilarity in blood, have proven to be incorrect. Blood is classified according to
  type, and all types are found within all supposed races of man. Blood
  transfusions are based on types A, B, AB, and O and are given without
  regard to race.4   It has also been supposed that different races have
  differing intelligence levels. The false and racist idea concludes
  that the Caucasian race is the most intelligent with the Negroid race
  being the least intelligent. 
  
  ...content removed...
  
  Modern testing of the races has shown that intelligence is not a measurement of race, because intelligence levels differ greatly with
  individuals within every race. Further cultural influence and
  advances account for most supposed examples of differing
  intelligence. 5


The concept of "race" isn't Biblical, either.


  The next question is "Can race be Biblically defined?" The term
  race does not appear in the Bible. The Bible refers to differing
  peoples in terms such as family, tribe, people and nation. It groups
  people according to familial relationships and then into
  nationalities. An example of familial relationship is found in Genesis
  10, where the genealogies listed are grouped by family. It should be
  noted that nowhere are the sons of Noah associated with race or color.
  An important passage on this matter is found in Genesis 10:5:
  
  "By these were the isles of the Gentiles divided in their lands; every one after his tongue, after their families, in their nations"
  (Gen. 10:5). 


The differences in skin color, hair color, curliness/straightness of the hair, and other traits that we, in our society call "different races" are minor variations. They can easily be attributed to simple genetic complexity -the same mechanism that causes my children to not look exactly like me, but similar to me, multiplied over many generations. As families became more spread out over the globe after the flood, the differences became more pronounced within the groups.