I am in a very small office and generally anything we do is during work hours. My boss will have parties at his place that we are all invited to (including partners/kids), but they have other people there as well.

A couple of times a year there are larger functions which are generally incorporated with a training session or AGM during the day, followed by a work people only dinner. I tend to go to them because they are held in various areas and I am away from home anyway. There was one in our area last month which I didn't attend, although I was suffering from a 2 day headache so felt fairly justified. They are usually fairly tame, lots of older people at my work.