bukatyne:
These complexes are new to me.

Growing up, four kinds of kids were the favorites irrespective of gender:

1. The first born
2. The last born
3. The only boy/girl
4. Best behavior/similar behaviour to liking parents.

Just a question:

Does the father/mother like all the daughters/sons or do they pick one?

Most times the father's favorite is the first daughter or only girl, for the mother it is the first son, only boy or last born boy/girl. Except there is a conscious effort by the parents to avoid this which i recommend.