Maternal breastfeeding and complementary feeding knowledge is an important determinant of childrens’ long-term health and development. This study aims to account for associations between knowledge and practices in Kenya and report the food consumption of children from birth to 18 months. In 2015 mother–child pairs were recruited from Mother-and-Child Health Centers; 415 in an urban slum in Nairobi and 364 in rural Machakos. Knowledge and practice scores were calculated from questionnaire variables and 24-h food frequency questionnaire. The associations of knowledge and practices were studied with regression analysis. Breastfeeding knowledge (Nairobi 6.3/9, Machakos 5.9/9) and practices (Nairobi 7.5/8, Machakos 7.2/8) were good in both areas. Complementary feeding knowledge was not as good (Nairobi 7.5/14, Machakos 7.1/14). Minimum meal frequency was reached by almost 80% of the children but dietary diversity was low (Nairobi 2.7 [SD 1.4], Machakos 2.4. [SD 1.3]). Only 27% of children in Nairobi and 13% in Machakos were fed a minimum acceptable diet. The complementary feeding knowledge score was associated only with minimum dietary diversity in Nairobi (OR: 1.29; 95% CI: 1.105–1.514). Infant and young child feeding knowledge and practices were on a similar level in both areas. Future interventions should focus on improving dietary diversity.