This paper aims at capturing the interrelation between two life course transitions linking the generation of elderly parents and their adult children: (early) retirement and the transition to grandparenthood. We contribute to the broader literature on the life course which theorizes the presence of crucial interdependencies of life domains and between related individuals over time. Our interest lies in the extent to which parents’ retirement decisions influence their adult children’s transition to parenthood, producing crossover effects across family members (parents and children) and spillover effects across life domains (employment and family). Parents’ early retirement might be pulled by the need to care for a grandchild; conversely, children transition to parenthood may be triggered by the availability of flexible, reliable and inexpensive care by retired parents. Drawing on the SHARE longitudinal data on more than 26,000 individuals from 21 countries and an event history approach, we model the reciprocal relationship between the arrival of the first grandchild and early retirement decisions in midlife, with specific attention to gender and socio-economic differences. Results show that becoming grandparent has a significant and positive effect on the risk of early retirement for both men and women. Highly educated newly grandfathers have a higher probability of an early retirement than those lower educated, while for grandmothers there is no educational gradient. Early retirement instead does not foster grandparenthood in a significant way, though the estimates by gender point at opposite directions: grandfather’s early retirement hinders his children’s transition to parenthood, while grandmother’s early retirement is positively associated to her children’s fertility. Our findings speak in favour of holistic life course policies considering spillover and crossover effects.