Theres a few secrets about beans stalks, first after your sim has been doing alotta magic, a special plant will appear. if its a small bean stalk itll start to grow. (my friend told me all this stuff from this point) once a beanstalk is big enough you can climb it to get magic beans. also, move into a magictown house with a beanstalk and a giant will walk by your home, but for no reason.