Marriage comes first
The family-planning sequence is post-marriage content. Continue playing after the wedding rather than expecting the option immediately at the altar.
Wait for the Mystical Feather
A cutscene in the weeks following marriage makes the Mystical Feather available and opens the optional family-planning discussion.
You can opt out
The official FAQ explicitly says the player has full control over whether to have a baby. This guide does not treat community speculation about appearance or timing as confirmed fact.
Primary sources
Checked against these public pages. Official sources define confirmed features and status; community sources are labelled as such and used for game data that the developer does not publish directly.