Thinking about families you never, or barely see on television helps I think. I went with a really mixed race family just because I've never seen that before and happen to be part of one, so I was inspired really fast. It also helps to think of the idea of a traditional family, and then think of how that's changed over the years. Things that were unheard of before and are now much more common.
Modern Family revolves around three separate families, mainly a mother and her husband who have three kids in a kind of dysfunctional family. I'm pretty sure those two had kids really early, I haven't seen the show in a while. There's also a gay couple who adopted a Vietnamese child, and a Colombian woman who has a tween son and remarried to an older man, then had another child with him. I haven't watched it in a while, though, but those are pretty good examples.
sweatdrop It's also actually possible for two women to
have a child on their own now, which could be a fun idea to play around with.
Maybe it'd be okay if someone did a single parent and an aunt or uncle who sometimes helps out?