letourneau and vili fualaau spoke to barbara walters in a 20/20 interview that will air friday .
couple 's 17-year-old daughter , audrey , was born while her mother was out on probation . her 16-year-old sister , georgia , was born behind bars .
letourneau and fualaau started a sexual relationship when she was his sixth-grade teacher and she fell pregnant with his child when he was 13 .
she served a few months in jail and fell pregnant with his second child within weeks ; she was then sent back to prison for seven years .
but a year after her release in 2004 , they married and are still together .
letourneau said there was never a big conversation with their daughters about the scandal because they grew up with it .
vili fualaau lamented that he did n't have the right support as a young father of two girls .