My perception of a 'Sportive' is that it involves some sort of competition. Usually on cyclosportives, the competition is against the clock.
Bike rides to attract new members to clubs, including families, have in my memory been short affairs where parents and children are not expected to ride any more than ten miles. To somewhere where the children can pester their parents for a bottle of pop and a bag of crisps.
40km ( 25 miles ) in my estimation won't attract families. Remember these 16" wheel bikes only top out at 10 - 12 mph on a flat stretch. This means the kids are gonna be in for 2 1/2 hours at least in the saddle. To a kid, that's a whole afternoon at school, and you know how long that seemed.
I have seen these kind of 10 mile 'introductory' rides advertised as 'Family fun rides' rather than something that implies an element of 'racing'.