What family does colts belong into?

Colts aren't in a family. They are the name of a young male horse, under the age of 4. Sometimes all baby horses are called colts, but the proper name for a male baby is colt, and the proper name for a female baby is filly. When they are age 4 and older, the male is called stallion (stud if he is used in breeding) or gelding if he has been neutered, and a female is called a mare.