Suppose parent 1 is male -
males tell the truth so the kid said 'I am a boy'.
Females alternate truth - there are two possibilities (TF) or (FT)
kid is a girl and did not lie - this is inconsistent with 'I am a boy'
kid is a boy and did lie - boys do not lie
conclusion: parent 1 is female
Parent 2 must be male due to the heterosexual restriction -
the statement of the female that the kid said it was a boy may be
true or false - we must discount it.
Males tell the truth so the kid is a girl and the kid lied. This is
consistent with females alternating truth telling.
This is the only possibility so the kid is a girl.