No, they're not gay.
Although lately I have the feeling that would be easier to explain to a three year old.
When I was 14 (?) my parents got divorced. My dad quickly got remarried. BUT I've never considered my stepmom my mom. At all. It probably has a lot to do with the fact that our families were friends while my parents (and my stepmom & her husband) were still married. Probably has a lot to do with the fact that my stepmom would call and ask us if my mom was home when she knew she wouldn't be and then just ask to hang out with me, my sister and my dad. Probably has a lot to do with the fact that my dad chose his new wife over his children and we didn't speak for a long while.
All of that is in the past though. I do get along with my stepmom and my dad just fine now. Sure, the relationship has its awkwardness but, for the most part, it's as normal as a relationship with your parents can be. They see the kids more than any of the grandparents since my dad is in town for business at least once a month.
Beanie was convinced my stepmom is my mom. I tried to explain that, no, Grandma L was my stepmom. That the other Grandma L was my mom. The concept of divorce is lost on Beanie. I'm glad she doesn't understand that right now. I try to explain that my mom and dad used to be married to each other, but now they are married to other people. I tell her that it means she gets an extra set of grandparents.
I don't think she really gets it. I suppose if the circumstances were different I really wouldn't care that Beanie thought I had "two moms." But, the way it all went down (even though it was over 15 years ago) makes it that I don't want Beanie to think my stepmom is my mom. It isn't really that big of a deal I guess. I'm sure in time she will understand better.
Do you have step-parents? How do you explain those relationships to your young children?