As a single parent, I told both of my daughters, ages 13 and 20. My 20 year old is away in college but is also my next of kin, so I told her. I explained to my 13 year old what I was doing and why. She is looking forward to when I dont have to be on medications and am healthier and happier. She is a willing participant and supportive to this journey. It was important to me that she understood the why more than the what.
But the bottomline is you know what your kids can or cannot handle.