M.R.
Dear C.: Don't worry! A Bakers Cyst goes away as they grow older. My 13 year old son had one when he was about 3 years old. I did a sonogram every year until it disappeared, and in the sonogram you could see how it kept getting smaller with time. He never felt it, and it never bothered him when he excercised, and he has always been in sports and is a great athlete. My doctor was never worried, so I did not worry two much, specially as we compared the size year after year.
At the time, I visited a pediatric orthopedic surgeon and he recommended that we kept watching it in case it grew in size, which would have been unlikely. He said he would not recommend surgery unless it bothered him to walk or excercise. Since he never complained, we never did it.