Instability in early childhood education and care (ECEC) arrangements may have detrimental consequences on children's mental health. This study examined ECEC trajectories in the first 30 months of life for 373 children from low-income families in Toronto. We provide information about patterns of instability and reasons for instability. We also tested whether instability in ECEC was related to children's mental health using the Strengths and Difficulties Questionnaire. Five main profiles of ECEC stability were identified: (1) 8% in Home-Only, (2) 56.3% in Home-Center, (3) 8.0% in Home-Center-Home, (4) 5.9% in In-and-Out, and (5) 20.9% in Home-Multiple-Centers. Frequently mentioned reasons for change were a new baby in the family, availability of grandparents, quality of ECEC and family relocation. Families in these different profiles had similar demographic characteristics. Of the five profiles, children in the Home-Center-Home profile had a significantly higher likelihood of experiencing mental health problems compared to the Home-Center and Home-Multiple-Centers groups. These findings have important implications for future research, policy and practice related to ECEC availability.