Let your boy keep moving and do not worry about it. Keep him away from Ipads
Take him to a playround and let him run himself off. At this age they cannot take instructions but they will do what you do, so if you run he will want to run, if you want to play he will play, if you do a burpee he may try to copy you....
Unless you are trying to build a super human kid to be something amazing with no life (like the Russians and Chinese do to their elite kids) then let him be a kid and keep him activated.
When the time comes later when he shows interest you will know. Kids can start to take instructions and remember them from about 6yrs of age.