I joined Intertel once, yet found that most of the members in my local area were people I already knew from Mensa. Mensa is far superior in terms of activities, numbers, and publications. There are many people in Mensa who might qualify for these other organizations, but as far as I know, none have enough numbers to compete with Mensa regional,national, and international gatherings and local events.
As far as kids go, most Mensa activities are open to all family once a single person joins. It doesn't matter if the Mensa member is a parent or child. Therefore, most kids at Mensa events are the offspring of members, as there is no real advantage to paying multiple dues.
