BackgroundPhysical activity (PA) is associated with positive health outcomes over the entire life course. Many community-based interventions that promote PA focus on implementing incremental changes to existing facilities and infrastructure. The objective of this study was to determine if such upgrades were associated with increases in children’s PA.MethodsTwo cohorts of 3- to 15-year-old children (n = 599) living in 4 low-income New Jersey cities were followed during 2- to 5-year periods from 2009 to 2017. Data on children’s PA were collected at 2 time points (T1 and T2) from each cohort using telephone survey of parents; data on changes to existing PA facilities were collected yearly from 2009 to 2017 using Open Public Records Act requests, publicly available data sources, and interviews with key stakeholders. PA changes were categorized into six domains (PA facility, park, trail, complete street, sidewalk, or bike lane) and coded as new opportunity, renovated opportunity, or amenity. A scale variable capturing all street-related upgrades (complete street, sidewalk, and bike lane) was constructed. PA was measured as the number of days per week the child engaged in at least 60 min of PA. The association between change in PA between T1 and T2, ranging from − 7 to + 7, and changes to the PA environment was modeled using weighted linear regression controlling for PA at T1, child age, sex, race, as well as household and neighborhood demographic and socioeconomic characteristics.ResultsWhile most measures of the changes to the PA environment were not associated with change in PA between T1 and T2, the street-related upgrades were positively associated with the change in PA; specifically, for each additional standard deviation in street upgrades within a 1-mile radius of their homes, the change in PA was 0.42 (95% CI: 0.02, 0.82; p = 0.039) additional days. This corresponds to an 11% increase over the mean baseline value (3.8 days).ConclusionsThe current study supports funding of projects aimed at improving streets and sidewalks in cities, as it was shown that incremental improvements to the PA environment near children’s homes will likely result in increased PA among children.