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Cigarguy Ok so here's how it works. You have a "Pack" that's the larger group of all ages. Then you have "Den"s which are the age groups broken down. A 7 and 10 year old will most likely be in different Dens, unless you have a super tiny Pack. So the whole Pack usually meet together, then break-out into Dens. The Den's work on advancements and achievements together, which is why they separate the age groups.
They typically have a bigger Pack event, maybe once a month. Like a campout. All Dens attend together, and Cubs need an adult to attend events like this with them. Adults don't have to attend weekly Den meetings, but it sure is helpful (and FUN!)
If they advance to Scouts after fifth grade, they can attend meetings and campouts without an adult partner.
And, yes, they have allowed girls into what used to be called "Boy Scouts" (including Cubs) but at the Pack level they have to have a female leader in order to allow girls.
Hope this helps.
PS. I sincerely hope you have an active Scouting community where you live. Where we live is very active in Scouting and it really made it exciting with the events they could plan.