I just came across this paper about GnRH analogues used in children with gender dysphoria.
academic.oup.com/jcem/article/100/2/E270/2814818
This suggests that the BMD (bone mineral density) was below their pretreatment potential and either attainment of peak bone mass has been delayed or peak bone mass itself is attenuated.
Despite these limitations, our findings are relevant given that most the patients currently treated in our clinic is late pubertal at start of GnRHa treatment, as is observed in other transgender populations (21, 22). If CSH is postponed beyond the age of 16 years it should be taken into account that these subjects may be particularly prone for loss of bone mass. In addition, concerns for possible long-term deficits in bone health may be amplified in subjects who present at a more “ideal” pubertal stage, ie, Tanner stage 2–3.
In short, expect children who are on these drugs to end up with crumbling bones. The younger they are when they start on the drugs, the worse this is likely to be.