middle child

plural middle children

1. human sciencesIn an immediate family containing three children, the child who is neither the oldest nor the youngest.

   As a middle child, you're not Mommy's big girl nor her little boy; you're just there.

   1987 February 15, Jean M. Sarosy, “Topics: The Unseen Woman”, in New York Times, retrieved 27 Apr 2014

   3 more examples

   I was the middle child of three, but there was a gap of five years on either side, and I barely saw my father before I was eight. For this and other reasons I was somewhat lonely.

   1946, George Orwell, Why I Write

   Elliott [is] the forgotten 10-year-old middle child between a teenager with a lot of friends and a precocious golden girl.

   2002 March 30, Richard Corliss, “That Old Feeling: "E.T." Goes Home”, in Time, retrieved 27 Apr 2014

   My husband is the classic middle child, the peacemaker often overlooked by his parents.

   2013 October 17, Carolyn Hax, “Tell Me About It: Middle-child syndrome, 2d generation”, in philly.com, retrieved 28 Apr 2014