The appropriateness of the questions is somewhat cultural. For instance in the US is generally considered impolite to ask how old someone is but not how many kids they have (or even the kids ages). In some other cultures, personal questions are a strong component of the cultural expectation in the workplace.
In all cultures however, at least some personal questions are considered ordinary and unexceptional.
In the company I work for we often bring offshore resources to this country and one of the reasons why is so that people develop personal relationships as we have found that it improves our ability to work together. This is true for most workplaces.
People who have some connection to each other personally generally work better together and people who try to remain too private in the personal lives tend to get excluded from the group and are not as effective at work as they could be. Co-workers often resent those who hide their personal lives because it makes them appear as if they think they are superior to their co-workers and look down on them. You don't want to appear to be a jackass to your co-workers.
Be polite and talk politely to people even if you choose not to answer their questions. If you don't want to talk about how many kids you have (I personally have never met a parent who didn't want to talk about his or her kids, but YMMV.), then change the subject to something less personal (but still not work-related) like the results of the football game last night.
This is not to say you have to reveal your whole life to anyone. Be friendly and make small talk at roughly the same level that everyone else does. The amount of sharing will also vary between professions and type of personalities. There are more introverts in the programming world than most professions, so you can get away with less sharing than if you are a sales person.
But it is counterproductive to be insulted at such questions as they are ordinary and unexceptional.