Gohan:Was born in The End oF Dragonball,because he was actually 5 1/2 years old
when Dragonball Z Just begon,so i think he was born in DB,But we never saw him in DB.
Parents:Goku & Chi Chi 

Trunks:Was born in the Training before the Androids came.He was born a year before
'they' came.
Parents:Bulma and Vegeta

Goten:He was born in The Cell Saga,but i think Chi Chi was pragnend of him
in the Android Saga.But i haven't seen Chi Chi ragnend so...
Parents:Chi Chi and Goku

Bra:I don't know Bra,but i think she was born in DBGT or in the Buu Saga.
Parents:Bulma and Vegeta

Pan:She was born in DBGT.She's a girl...NFI...	
Parents:Gohan And Videl