You'll have to 'bite the bullet' for a while, but this will quiet down eventually. The important thing is to stck with his usual routine and continue to insist that he go to sleep and remain in his own bed. If you alter the routine, it will be difficult to reinstate the routine at a later time. While it's not the best option to remain with him until he falls asleep (because then he's relying on that as a usual part of the routine), if his mother is going to do it she should simply sit in a chair near to, but not right next to, his bed.