Does anyone know the cost for a 8yr old for one year and for a 3yr old for a year?

I'd try getting a family plan. They are listed at $109.95 for basic, the plus family plan lists for $159.95. And you may be able to take a friend as a guest. Costs have gone up recently but it's well worth the investment!

Annual memberships aren't cost effective individually; two individual memberships are more than the family membership. It's definitely worth it if you go more than once in a year! Review options here: http://www.dmns.org/join/memberships/levels-and-benefits/

There doesn't appear to be a list price per person. It seems like there's only 2 membership packages. Heres a link to their website relating to your question http://www.dmns.org/join/young-professional-membership/levels-and-benefits/