In the original Harvest Moon game, you can have up to two children with your spouse.
First Child Requirements
- Both house upgrades
- Married for 20 days
- Wife's affection score is over 450 (7 hearts in diary)
Second Child Requirements
- First child is 31 days old
- Wife's affection score is over 650 (9 hearts in diary)
Once your wife tells you she's pregnant, the child will be born 60 days later. From the date of marriage, assuming you meet the requirements, it will take 80 days (almost 3 full seasons) to have your first child.