If my future kids (Hi there!) found my posts, I would be happy to share them. It wouldn't change what I post, but I'm fairly candid when posting already. There's nothing I wouldn't want them to see. My MSN conversations on the other hand...
It all comes down to how you write about something when you express yourself. When you want to say something about a situation, you want to express how you feel, what you see from the situation and anything that applies to you. Anything you say about the situation should be objective, or relate to only yourself. If you are posting about someone else, then don't demonise them, and don't call them names or put them down. Just express how they impact apon you.
It comes down to avoiding gossip, gossip being: talking about a person in such a way that it unfairly diminishes them. You can talk about people all you like, but you don't have to unfaily diminish them.
As for being too open, well, that's a whole different matter entirely. How open do you really want to be, and how much do you want people to get to know the real you.