Julia, the qualitative study of Steensma (2010) brings some light to the desistence myth in children. The study points that:
Although both persisters and desisters were quite similar in their gender atypical interests, preferences and behaviours, there was also a difference. This seemed to be subtle and belong to the area of underlying motives rather than overt behaviour. The persisters attributed their gender dysphoria primarily to the discrepancy between their body and their gender identity and a true longing for having a different body. The desisters, however, indicated that their desire to have the body of the other sex (if present at all) or the desire to be the other sex was more related to the opportunity to fulfil the preferred gender role, than to a true aversion against their bodies per se.
So the underlying motivation is different.
The study also asks for prudence because the experiences can be biased because of recall. But I think that is a study that helps to understand the desistence myth.