To validate the modified System for Observing Fitness Instruction Time to measure teacher practices related to physical activity promotion (SOFIT+) in physical education (PE) amongst 5-6-year-old-children. Participants (n = 162, 53% female, 6.0 ± 0.3 yrs) were recruited from 9 schools. Video-recordings of 45 PE lessons from 9 teachers/coaches were coded using a modified SOFIT+. Accelerometers measured children's moderate-to-vigorous physical activity (MVPA). Validity was assessed via multinomial regression measuring the relationship of both SOFIT+ index score and individual teaching practices with children's MVPA. Inter-rater reliability was examined. A 1 unit increase in the SOFIT+ index was associated with increased likelihood to engage in 10-19 sec, 20-29 sec and 30-40 sec of MVPA, compared to 0-10 sec. Most of the observed teaching practices were significantly related to children's MVPA. Inter-rater percentage of agreement ranged between 88.8% and 99.7%. SOFIT+ is a valid and reliable assessment of teaching practices related to MVPA promotion in PE amongst 5-6-year-old-children.