Small businesses are usually receptive to a pitch from a new grad for such an internship. For example, your daughter who wants to be an accountant might pitch herself as an unpaid intern for three months to a small accounting firm in your area.
Register with temp agencies in your area. It might require performing tasks that aren't exactly what he or she envisioned post-college, but it could be a foot in the door. Maybe there is even a task or two connected to the family business that you can assign.
Consider volunteering on a local political campaign. This is a great way to get thrown right in, gain experience and make solid contacts.
Do not opt to go back to school as a temporary solution, and don't stay in school simply because you can't find a job. If you're considering a graduate degree, it should be because you have a serious interest in a particular career path. Grad school, especially given the cost, is not simply a reason to prolong the inevitable job search.
Finally, demand some rent money -- a realistic amount, which may be nominal but it's symbolic of adult responsibilities. You can opt to use it toward household expenses or to create a savings fund for your son or daughter.
Be patient. Right now isn't the time for mom or dad to rush their kids out of the house. Off the couch, yes, but given the unstable job market not out of the house, especially if you have space at home.
Of course they're absolutely desperate to live on their own -- no new grad is thrilled to stay with mommy. They want the freedom to finally be on their own, but there's a lifetime ahead for that. (By the way, this is a delicate topic that several parents in my new Job Club group on MomsLikeMe.com have emailed me about. I know it's not an easy decision.)
Just remind them that staying with mom and dad for a bit longer than ideal enables them to begin paying off student debt and/or save money until they've got a cushion and feel confident about the job market.