If you're going to a Woodchip group, parents are almost always required to stay.
Parents are not usually required to stay in other groups. In fact, many groups discourage parents from staying if they are not helping out with the group. Having an 'audience' of parents can be distracting for both children and leaders. That said, most groups rely on some parental involvement, so parents may need to volunteer to stick around sometimes to keep the group running.