Some stories...
1. A few years ago a sister told me a story about how she had a chapter sister that actually had like a 3-4 year old when she joined ADPi.
2. Back in 2001, when I was at ASU, I met one of the newest Alpha member (on 9/11 ironically). Very sweet girl. We got to talking and she told me that she was like 23-25 years old and she had just started college. My sisters (I didn't affliate with that ASU chapter), obviously saw something in her and didn't look at her age. She was an amazing asset to the chapter.
I give these "stories" saying that it can happen, it just truly depends on the climate of the campus. Plus, it depends on the chapter and if they are "willing" to accept that there will be times that your child will come first in your life and not the chapter.
Not knowing much about your campus or the greek life on it, I say go for it. But be honest and open with the chapters. They are either going to want you for you or not and if they don't, well look at this way, it's their loss not yours