Early childhood caries (ECC) is the most common non-communicable disease among children worldwide. In New Zealand, ECC among Pacific children is significant and pervasive. Toothbrushing twice daily is an effective self-care measure for preventing ECC. However, no studies have investigated longitudinal patterns of toothbrushing. Additionally, no studies have investigated personal and family characteristics associated with childhood toothbrushing behaviours among Pacific children. This research aimed to investigate childhood toothbrushing behaviours among Pacific children in New Zealand and determine whether toothbrushing behaviours are associated with personal and family characteristics. The first objective of this study was to identify and describe early childhood toothbrushing trajectories among Pacific children in New Zealand. The second objective was to investigate the strengths of association between toothbrushing behaviours and personal and family characteristics. A quantitative methodology was utilised to conduct data analysis from a birth cohort study, the Pacific Islands Families (PIF) Study. The current study analysed personal and family characteristics data from the 6-weeks postpartum, 1, 2, 4, 6 and 9-year phases of the longitudinal PIF study. Group-based trajectory modelling was used to assign children into distinct groups based on their toothbrushing frequencies reported at ages 4, 6 and 9-years. Multinomial logistic regression was performed to examine the strength of potential personal and family characteristics with the toothbrushing trajectories. Four distinctive trajectories of toothbrushing behaviours were identified: these were characterised as ‘adoption’ (19.3%), in which children adopted the favourable behaviour of brushing twice daily; ‘cessation’ (15.7%), in which children stopped brushing twice daily; ‘consistent’ (21.9%), in which children brushed twice daily at all ages; and ‘inconsistent’ (43.1%), in which children had mixed brushing frequencies. After controlling for personal and family characteristics, children of mothers who brushed twice daily had a lower risk of following the ‘adoption’ trajectory than the ‘consistent’, which was also true for children in home-owning families. Male children had a higher risk of following the ‘inconsistent’ toothbrushing trajectory than the ‘consistent’, relative to female children. Children of 2 mothers brushing at least once daily, children using children’s toothpaste, and children with higher maternal education had a lower risk of following the ‘inconsistent’ trajectory than the ‘consistent’. Children of mothers who economised on fruit and vegetables at ages 4 and 9years were significantly more likely to follow an unfavourable toothbrushing trajectory than those who never had to economise. This study established that four distinct trajectories of toothbrushing can exist among Pacific children in New Zealand and were closely associated with parents’ socioeconomic advantage and mothers’ oral self-care behaviours. The findings provide stakeholders, such as policymakers, with evidence to remove financial barriers to toothbrushing. The findings also suggest that toothbrushing behaviour interventions targeting young children should focus on both the children and their caregivers, particularly novice or socioeconomically disadvantaged mothers. Further research examining toothbrushing trajectories into adulthood and associated oral health outcomes among Pacific peoples in New Zealand will help to better understand the current study’s findings.