Well, can he take them to classes after school?
Or, find something the kids can take, that occurs on weekends.
My daughter, takes Karate.. She is 7. The class is twice a week, weekdays, in the evening. So, for me, that is enough 'classes' after school. I don't want to over-schedule her... and homework and family time is important too.
If she does not do homework... she does not go to Karate.
So, she has learned time management and responsibility that way. Because she LOVES her Karate classes.
My son is just turned 4, but he is not in any 'classes.'
For my friends who are working Moms.... their kids take classes on the weekends. So weekends are busy. But "you" are the one's that decides how many classes they take and how much time that will take up, in your lives, on weekends.
And during the week, their kids are in the after-school care programs... where the working parents pick up their kids at about 5:00pm, and the schools also have some after school classes kids can sign up for...on campus. So, try looking into that too, as an option.
all the best,
Susan