I made a bassinet bonnet by covering an egg pan in royal icing and then sliding it off and adding to a cake. I am not sure if you want the cake to be the cradle or if you want a cradle on the cake...so I just thought that I would throw it out there! Good luck with your cake!
Check the template section in the galleries. I would bet there is a cradle template there. I made a gumpaste cradle a few years back. I purchase a little wooden cradle at Michaels. I carefully took it apart and used it as my template.