Children can be considered as a marriage-specific investment that increases the value of the marriage, making a divorce more costly. We exploit the richness of pre- and post-marital information from the National Longitudinal Survey of Youth 79, for the United States, to investigate the relation between fertility and marriage instability. In our model of marriage breakdown, we use the number of siblings of the respondent and, alternatively, multiple births, to instrument the number of children conceived during first marriage. Our results indicate that the presence of children significantly reduces the probability of marital disruption. In addition, the younger the children, the greater the deterrent effect. In contrast, we conclude that children conceived before first marriage increase the risk of marital disruption. Finally, the higher the parents' level of education, the larger the positive effect of fertility on marital stability.