Northern Italy has been the first European area affected by the COVID-19 pandemic and related social restrictive measures. We sought to evaluate the impact of the COVID-19 outbreak on PICU admissions in Northern Italy, using data from the Italian Network of Pediatric Intensive Care Units Registry. We included all patients admitted to 4 PICUs from 8-weeks-before to 8-weeks-after February 24th, 2020, and those admitted in the same period in 2019. Incidence rate ratios (IRR) evaluating incidence rate differences between pre- and post-COVID-19 periods in 2020 (IRR-1), as well as between the post-COVID-19-period with the same period in 2019 (IRR-2), were computed using zero-inflated negative binomial or Poisson regression modeling. A total of 1001 admissions were included. The number of PICU admissions significantly decreased during the COVID-19 outbreak compared to pre-COVID-19 and compared to the same period in 2020 (IRR-1 0.63 [95%CI 0.50–0.79]; IRR-2 0.70 [CI 0.57–0.91]). Unplanned and medical admissions significantly decreased (IRR-1 0.60 [CI 0.46–0.70]; IRR-2 0.67 [CI 0.51–0.89]; and IRR-1 0.52, [CI 0.40–0.67]; IRR-2 0.77 [CI 0.58–1.00], respectively). Intra-hospital, planned (potentially delayed by at least 12 h), and surgical admissions did not significantly change. Patients admitted for respiratory failure significantly decreased (IRR-1 0.55 [CI 0.37–0.77]; IRR-2 0.48 [CI 0.33–0.69]). Conclusions: Unplanned and medical PICU admissions significantly decreased during COVID-19 outbreak, especially those for respiratory failure.What is Known:• Northern Italy has been the first European area affected by the COVID-19 pandemic.• Although children are relatively spared from the severe COVID-19 disease, the pediatric care system has been affected by social restrictive measures, with a reported 73–88% reduction in pediatric emergency department admissions.What is New:• Unplanned and medical PICU admissions significantly decreased during the COVID-19 outbreak compared to pre-COVID-19 and to the same period in 2019, especially those for respiratory failure. Further studies are needed to identify associated factors and new prevention strategies. Electronic supplementary material The online version of this article (10.1007/s00431-020-03832-z) contains supplementary material, which is available to authorized users.