How dangerous is dental surgery on a 5-year-old?

Safe: If we are talking sedation, it is very safe when two doctors are involved. One to perform the actual treatment and another, called an anesthesiologist, to perform and monitor the sedation.

It depends: If you mean or surgery under general sedation, the risk from the sedation is probably more risky than any specific dental procedure. Please feel free to be more specific with your question.

With consideration: All surgery carries with it some risk. Dentists try to avoid surgery (fillings, extractions, root canal rx, jaw surgery, gum surgery) wherever possible. That's why your dentist spends so much time instructing you on oral hygiene techniques. If infection is present, however, surgery may be the only option. The surgery is less risky than the spread of the infection. If recommended, have it done.