Well, yes, some parents would. Some simply care about people more than others do. It's a continuum. I know individuals who would gladly take the opportunity of an employer paying them their normal professional salary while volunteering in such places. All these people happen to have their own children (this may be a coincidence, as I am old enough for most of my friends to have had kids by now).

The point is that there is, I expect, a strong inverse relationship between bitterness expressed by childless employees who don't receive paid time off their day job and the desire to volunteer to help others.