We estimate the causal effects of regular and occasional grandchild care on the depression of grandmothers and grandfathers, using data from the Survey on Health, Ageing and Retirement in Europe and an instrumental variables strategy which exploits the variation in the timing of interviews across individuals and the fact that childcare declines with the age of grandchildren. We find that 10 additional hours of childcare per month, a 31 percent increase with respect to the sample average, increases the probability of developing depressive symptoms by 3.0 to 3.2 percentage points for grandmothers and by 5.4 to 5.9 percentage points for grandfathers. These results suggest that policies that substitute informal with formal childcare can improve the mental wellbeing of grandparents.