Hi April! Have you checked out Meetup.com? Here's a link to Meetup groups near Honolulu. I am a member of C.O.F.F.E.E., which is for all of Oahu...not only Central Oahu as its name implies. I'm also familiar with Active Moms. Hope you and Sebastian find a group that suits you!
We just started the Tiny Tots program at our neighborhood park. It's a parent-child interaction program, and I am really happy with ours so far. Many of them are free or low-cost and run for a semester at a time. Check out the Honolulu parks and rec website and search for programs at your park of choice. Ours is 18 months and up, but the ages also vary from site to site. You can also try the Baby ***, but I tried them and never heard back about joining a group. Good luck!
Re: Playgroups?