This thesis addresses the following research questions: 1) what are the intensities of physical activities that are typically considered to develop motor competence in children, 2) how is accelerometer-derived physical activity (PA) associated with motor competence (MC), 3) what is the effect of family-based PA counseling on children’s PA and MC, and 4) does initial parental support of a child’s PA moderate the counseling effect on the child’s PA? Participants consisted of a total of 126 apparently typically developing children aged 4 to 8 attending childcare or primary school. PA was measured with triaxial accelerometers, MC with the Körperkoordinationstest für Kinder (KTK) test (Kiphard & Schilling 2007) and a throw-and-catch a ball test (Numminen 1995), and parental support with a self-report questionnaire (Cleland et al. 2011). Correlations were calculated and effects of intervention on study outcomes were tested by means of a linear mixed-effects model fit by REML and by a Mann-Whitney U test with statistical software. As a result, typical indoor physical activities were found to cover the whole spectrum of PA intensities, from sedentary to vigorous. MC correlated with moderate-to-high neuromuscular impacts and PA of vigorous metabolic intensity in 7–8-year-old girls, with high impacts in 5–6-year-old girls, and with moderate impacts and light-to- vigorous PA in 5–6-year-old boys. Associations between high neuromuscular impacts with the MC in girls requires further research, as the finding is novel and may reveal this developmentally important relationship to differ between the sexes. In general, tailored counseling was found to decrease the moderate-to-vigorous PA in the intervention children in comparison to the control children. However, children’s PA in the tertile of lowest initial parental support showed a significant positive intervention effect during the 6-month counseling period, although the change was not maintained at the 12-month follow-up. Counseling during an inactive season provided a significant effect on the development of children’s KTK performance during the follow-up phase. In conclusion, because physical activities that are important for motor development contain a wide range of intensities, from sedentary to vigorous PA categories, there is a need to communicate (e.g. via PA guidelines) the developmental role of PA of different intensities. Considering the two methodological approaches used in this study, there is a need for more sophisticated objective PA assessment methods to differentiate real sedentary behavior from significant PA patterns inducing low accelerations. Regarding PA counseling, screening and counseling parents who provide low support for their children’s PA could offer a feasible and efficient PA enhancement strategy in 4–7-year- old children. While a focus on motor development may serve to meaningfully supplement PA enhancement in children, initiation of PA counseling during the inactive season may induce a more sustainable effect on the development of MC.