I am homeschooling my almost 6 year old (kindergarten) and this is the first year we have been serious about it. Before this we did preschool like stuff at home and had lots of playdates with other kids doing crafts and such. Since I am only starting out on this adventure I only have a couple suggestions; the first is HSA - Home School Support Association, they are mostly a Yahoo group that has smaller chapters all over the area, most are in the South King County area, they plan activities and provide support for homeschooling families and are not religious based.
I would try the Washington Homeschool Organization for more information. I would also try joining a Mom's group, I belong to the Renton Moms Group which is a Meetup group (not a homeschool group but your kids are young enough to still enjoy just playdates) and have met a ton of great Moms and they have a lot of playdates and other activities so the kids get out and get socialized. There are also other Meetup and Yahoo groups specifically for homeschooling but I haven't found that many that aren't religious based.
You can also check out alternative learning programs offered by the state, it isn't "technically" homeschooling but you are at home teaching your kids with your values and ideals with support from a certified teacher and some funding to help pay for supplies and curriculum. A few to look at are CVA and k12. The Washington Homeschool Organization has more information about alternative learning programs as well, the pros and cons and the requirements. I went this route mostly to help pay for supplies and curriculum and I also wanted to make sure I am keeping up to standards for my sons learning since I am a list kind of person, some people don't like the requirements or not being able to teach only what they want when they want but since my curriculum isn't religious based I have had no problems.
I hope this helps a little, I was confused and overwhelmed at first too but socialization has been the least of our problems! Good Luck! Feel free to contact me if you want.