Theory behind 1st child 5th house

[sroo]

I'm looking for the theory behind that the first child is symbolised by the 5th house and the second one symbolised by the 7th.

I can create some logic. So, it could have been that the first child is symbolised by the 5th house because the first child was often concieved when the marriage was new and the couple in love. Their creative spirits and self expression was high. Whereas the second child is concieved when the marriage is balanced and matured into an order of stability and ways to live each day with eachother.

If this is true, it would mean the logic sprung out of cultural norms of conception and family creation. It's not unheard of, as with the old notion of Venus symbolising the spouse of men and mars symbolising the spouse of women. As culture have enabled both sexes to embody both these energies in modern times the way the planets impact us has changed with culture.

If children have the same link to culture in horoscope interpretations. We might have to investigate how a person concieved their child or the family setting to know which house is symbolising the specific child.

Though it would be wonderful to find the origin of the theory to understand the bases. It might be something more. Or different that sheds a completely new light on it.

[t5]

My personal view is that houses 1 to 4 establish our family values/conditioning and house 5 is where we begin to move beyond them. … Thus, the 5th = personal creations for which we would sacrifice our conditioned views. The first born thus establishes us as a parent, whist previously our experience of life is solely as a child.

The second child is then the sibling of the first born, which is the 3rd house of the latter’s chart … and the 3rd from the 5th in our own chart. The 3rd from the 5th being the 7th.

[Ava]

My first child was conceived right after I got married or on my honeymoon. My 5H cusp is in Sag, most of my 5th house is Sag.

Anyway, as it was our honeymoon, we were traveling (Sag theme). Transiting sun in Aries was applying to my Jupiter (Sag ruler).

Our Sag son was born less than 9 months later. His sun falls in my 5th and transiting Jupiter was right on my MC. (His sun is also conjunct draconic Jupiter. Coincidentally, as I write this, the transiting sun is conjunct draconic Jupiter in Sag.)

That's all straightforward.

Conversely, I cannot see how my daughter is signified by the 7th house, except that her Aqua Uranus falls in my 7th and squares her Scorpio sun (which falls in my 4th house).

Pls don't quote

[t5]

www.astro.com/astrowiki/en/Derived_Houses

[lumina]

it comes from medieval astrology, the 5th house is the 11th house counted from 7th house. 11th house originally was seen as "goals/ hopes in life", the goal of marriage (7th house) was to have children (5th house). At least that is one way how to arrive at this. There are probably other theories on that. I like the honeymoon one.