I am...
an only child.
the eldest child; my siblings are all of the same gender as me.
the eldest child; my siblings are not all of the same gender as me.
a middle child; my siblings are not all of the same gender as me.
a middle child; my siblings are all of the same gender as me.
the youngest child; my siblings are all of the same gender as me.
the youngest child; my siblings are not all of the same gender as me.