I didn't get much response last time so am assuming others have not found anything that works.
I have a big problem washing my son's hair. He is three. He is frightened. Jumps out of the bath (it is a small plastic one) and is shaking. I have tried the shower and that worked for a short time. He screams and shouts. Short of physically restraining him (which I don't like) I find it impossible. I have tried bribes.
I take him swimming and then at least he gets his hair wet. He enjoys swimming and although not floating is confident.
The problem extends to haircutting. We have visited a kind and patient hairdresser twice but the actual haircut didn't eventuate as my son was too distraught.