Any=better than none
It is very hard to get children
age 4-12 into a structured exercise
unless they are in a sports team such as soccer/field hockey etc.
..Because not doing it with other children=borning and thus they won't do it for long, not for health reason. They need fun along with it. Just because u think it is good, does not mean they do. So, get them involved with other kids, any =better than none. Good luck.