Raised alongside your dwarven kin, be it within the gemstone and gold gilded halls of their magnificent keeps beneath the mountains, or as a child of a simple dwarf blacksmith or miner amongst the world of men. Your upbringing has left you with some characteristics like that of your dwarven kin.

Your Constitution score increases by 1 and you choose whether your Strength or Dexterity score increases by 1

A dwarfling reaches adulthood at the age of 20 and generally lives to be about 400.

Most Dwaflings are lawful, with a strong moral compass for what they believe is right and fair. Whether they are stern like their Dwarven kin or more compassionate like their Halfling kin, is purely up to which has a stronger influence on their earlier year. Normally they adopt a balance between the two.

Dwarflings average about 4 feet tall and weigh about 100 pounds. Your size is Small.

Your base walking speed is 25 feet.

When you roll a 1 on the d20 for an attack roll, ability check, or saving throw, you can reroll the die and must use the new roll.

You have advantage on saving throws against being frightened.

You can move through the space of any creature that is of a size larger than yours.

You can speak, read, and write Common, Halfling and Dwarvish. 
Dwarvish is full of hard consonants and guttural sounds, and those characteristics spill over into whatever other language a dwarf might speak.
The Halfling language isn’t secret, but halflings are loath to share it with others. They write very little, so they don’t have a rich body of literature. Their oral tradition, however, is very strong. Almost all halflings speak Common to converse with the people in whose lands they dwell or through which they are travelling.