In this 100-daily diary study, we examined how affect intensity and variability of adolescents (N=159, Mage=13.3) and parents (N=159, Mage=45.3) changed after the onset and during (>50 days) the second COVID-19 lockdown in the Netherlands. Using preregistered piecewise growth models, we found only an unexpected increase in parents’ positive affect intensity after the lockdown onset (difference=1.75, p=.005), but no changes in negative affect intensity or variability. Both adolescents and parents reported gradual increases in negative affect intensity and variability as the lockdown prolonged (Mslope=0.44-0.67, p<.008). Yet, we found individual differences, which were partly explained by life satisfaction, depressive symptoms, and self-reported lockdown impact. Overall, our findings suggest that a lockdown might trigger changes in affective well-being, especially as it prolongs.