Which is the title of duke’s kids?

Question

For example the kids of Duke of Albany or Duke of Montrose they called (I mean title)

Answer 1

The children would be called either Lord X or Lady Y.  Depending on the ducal title - the eldest son of the Duke might have what is called a "courtesy title" to distinguish him as the presumptive heir.  

For example -- The Duke of Argyll is Torquhil Ian Campbell (who is the current title holder.)  He has two sons --  the eldest Archibald Frederick Campbell who is the Marquess of Lorne and a second son who is Lord Rory James Campbell

The courtesy title for the Duke's eldest son and heir is the Marquess of Kintyre and Lorne.

Answer 2

The eldest son of a duke takes on his father's next title down,so he is "The Most Honorable,The Marquess of --"and is called "Lord Title Name."The title name depends on what he is Marquess of;if he is Marquess Tentwhistle,he can be addressed as Lord Tentwhistle.

A duke's daughters are "The Lady Given Name Surname" and are addressed as Lady ---. Younger sons are "The Lord Given Name Surname," and are addressed as Lord ---.