You don't know that the kids are happy. I'm reminded of the gymnastics coaches Bella and Martha Karolyi, who reportedly were harsh on their athletes. They apparently encouraged starvation/anorexia, and taught their gymnasts that eating was a weakness. That is according to Joan Ryan's book "Little Girls in Pretty Boxes". The author said that at one Olympics, Karolyi's gymnasts had food smuggled into their dormitory. The coaches apparently also forced their athletes to work when injured, with the support of the team doctor. I remember a documentary in which Bella said "Just don't let them out of the gym. If you do, they might not to come back".
Anyway, the author noted that although the Karolyis' questionable methods were well know, parents still wanted to send their kids to them - the reason being, they were known to produce champions.
Parents always don't do what is in the best interest of the child, especially when they have a whole lot invested in the success of the child.