Intervention group will receive the Run Daddy Run intervention.

Intervention group will not receive the Run Daddy Run intervention.

The Run Daddy Run intervention will consist of 5 (inter)active sessions for fathers and their children + 1 follow-up session, each session lasting 90 minutes. These sessions will be given to 8 groups of +- 13 families (fathers and their children), guided by 2 facilitators and will take place every 2 weeks, at a location in the neighborhood of fathers and children (e.g. school of the children). Additionally, a website will be available for the fathers and their children, with additional information about the project, tips and information about being active together (e.g. movement breaks, fundamental movement skills, etc.) and limiting screen time. In addition, fathers and their children will also log their goals on this website, and between two sessions (= a period of 2 weeks) they will be asked to keep track of their co-PA on this website, aiming to reach their goal.

Father-child co-physical activity, will be subjectively measured using a seven-day recall diary, in which fathers will be asked to report all physical activities and screen time activities they performed together with their child in the last 7 days. More specifically, fathers have to report the start hour of the activity/activities, duration of the activity/activities, and the activity/activities itself in this diary, for each day of the week. PA diaries are often economical and can provide information on the types of activity not recorded from more objective measurement methods, such as accelerometers [66]. According to Matthews et al. (2002), diary based self-reported instruments can provide, with good participation compliance, accurate and valid assessments of PA [67].

Objective PA data will be collected through accelerometry. Axivity's (model AX3, 3-axial) will be worn by the father and the child for at least 7 consecutive days, on the non-dominant hand, for 24 hours a day. Participants' light (LPA), moderate (MPA), vigorous (VPA) and total PA will be assessed during this time period, which have been shown to be reliable and valid [60]. As an additional measure of (self-report) PA, fathers will be asked to complete the International Physical Activity Questionnaire Short Form (IPAQ-SF), for both himself and his child, questioning LPA, MPA and VPA during the past seven days [61, 62].Research comparing the IPAQ-SF with objective measures (i.e. accelerometers) shows that the criterion validity of this questionnaire is fair to good, with an ICC 0.30 [62]. Overall, the IPAQ-SF has reasonable (test-retest) reliability (ICC=0.65) a good internal consistency (Cronbach's Alpha=0.83) [63].

Objective PA data will be collected through accelerometry. Axivity's (model AX3, 3-axial) will be worn by the father and the child for at least 7 consecutive days, on the non-dominant hand, for 24 hours a day. Participants' light (LPA), moderate (MPA), vigorous (VPA) and total PA will be assessed during this time period, which have been shown to be reliable and valid [60]. As an additional measure of (self-report) PA, fathers will be asked to complete the International Physical Activity Questionnaire Short Form (IPAQ-SF), for both himself and his child, questioning LPA, MPA and VPA during the past seven days [61, 62].Research comparing the IPAQ-SF with objective measures (i.e. accelerometers) shows that the criterion validity of this questionnaire is fair to good, with an ICC 0.30 [62]. Overall, the IPAQ-SF has reasonable (test-retest) reliability (ICC=0.65) a good internal consistency (Cronbach's Alpha=0.83) [63].

Co-ST will be measured using a seven-day recall diary, in which fathers will be asked to report all physical activities and screen time activities they performed together with their child in the last 7 days. More specifically, fathers have to report the start hour of the activity/activities, duration of the activity/activities, and the activity/activities itself in this diary, for each day of the week. PA diaries are often economical and can provide information on the types of activity not recorded from more objective measurement methods, such as accelerometers [66]. According to Matthews et al. (2002), diary based self-reported instruments can provide, with good participation compliance, accurate and valid assessments of PA [67].