Try setting up a Klub Kindergarten..get the k-parents to run it--have them meet 1x month-do educational activites every other month(get ideas from teacher-(some our tchr has used is alpa drwing in sand, rice etc..) and fun in between--movie night--nature walks--bingo night(use alphabet bingo)
At our kindergarten orientation for the parents our Principle(who is very,very supportive of us)talks about all the programs the PTA brings into the school and all we do for the kids and their families. We have committee sign-up sheets there for parents to take, fill-out and send back to me.
Then at our kindergarten orientation for kids he comes down again and speaks to them again about the school and PTA.
And yet again at back to school night he does it again just for the heck of it. Since it comes from him and not PTA it holds more weight.
During our Kindergarten Round-up in the spring, we put together a packet with our brochure and an invitation for the parents to join us at our Spring Carnival and the remainder of our meetings for the year(make sure to include dates). A PTO rep also speaks for a few minutes at each of the sessions. Then at registration we have a table with our brochures, other information, and a calendar of events that tells about our Boo-Hoo Breakfast, Open House activities and first meeting of the year. We try to have the table staffed so there is a friendly face to answer questions about the organization or anything else parents may want to know about. The school is very kind to place us first in the line of tables for registration so parents CAN'T ignore us.
The biggest thing is to make sure that you are out there promoting your group so you're not a mysterious entity to these potential new members. Make sure any brochure you use describes your fundraisers, the programs you support and how to get involved.