This paper examines how a mother’s well-being during her first experience of motherhood influences both her desire for and likelihood of having a second child. Using data from the UK Millennium Cohort Study, it analyzes mothers’ emotional states when their first child is approximately nine months old, focusing on four key factors: emotional support from their partner, life satisfaction, frequent tiredness, and experiences of misery or depression. The findings indicate that greater partner support and higher life satisfaction positively affect both the desire for a second child and the probability of having one, as shown by longitudinal data. In contrast, frequent tiredness is associated with a lower desire of expanding the family. The study further explores how these emotional states are shaped by broader life circumstances, including work conditions, financial concerns, and the partner’s involvement in domestic and caregiving responsibilities, highlighting the complex interplay between emotional well-being, uncertainty, and fertility decisions.