Background It is well recognised that the period between birth and 2 years of age is a critical window to promote health and development, and prevent stunting. In most countries, the majority of the decline in length-for-age during the first 2 years of life occurs during the complementary feeding period, between 6 and 24 months of age. Prevalence of optimal complementary feeding practices are lower than expected. Undernutrition contributes 35% of child mortality. Poor complementary feeding of children aged 6 to 24 months contributes to the characteristic negative trends and deaths observed in developing countries.

Methods This is a community-based cross-sectional descriptive study using a semi-structured questionnaire which was interviewer-administered to 380 mothers of children aged 6 to 24 months in the community. Multi-stage sampling was used to select the study participants. Epi-info version 7 was used to analyse the data.

Results Of the mothers interviewed, 50.79% of them reported good knowledge; 66.84% had good attitude and only 25.26% had good practice of complementary feeding. The significant factors affecting complementary feeding practice were mothers’ educational status (p-value=0.0005); antenatal clinic visits (p-value=0.0006); and household monthly income (p-value =0.0000)

Conclusion The results of this study indicate that complementary feeding practices are suboptimal in Mushin local government of Lagos, Nigeria. In addition, there is knowledge-practice gap among the mothers owing to factors such as mothers’ educational status, household income and antenatal clinic visits.