I don't think we should be assuming that a two year time limit is designed to demonstrate happiness, TBH. Yes, we absolutely need longitudinal studies so that we have evidence of what happens 10, 20, 30 years post treatment. But the short term negative effects of gnrh analogues are pretty unpleasant. It requires a regular deep muscle injection which is painful enough as an adult, never mind as a child. Headaches, joint pain, bone pain, insomnia, hair loss, night sweats. The first time I was put on them, when my hormone levels tanked (which took about 3 weeks), I spent several hours hiding under the duvet because I could see teeth climbing out of the walls. They make you feel absolutely rubbish. So I'm not convinced that a child who is on them will say they feel happy if regularly assessed over a two year period.
If they can prove negative effects in a two year study, that gives a much quicker pathway to banning them for this cohort in all circumstances. What does worry me is that children will continue to be told that it doesn't matter how they feel on these drugs because as soon as they take cross sex hormones they'll feel better. Which begs the question, I suppose, of whether or not children (and parents) consented to cross sex hormones in an attempt to escape the misery of gnrh analogues.
They would also need a control group who were given a placebo to compare with the group given gnrh analogues, because it's likely that children who have been groomed online to believe that this medical pathway will solve all their problems will see some uplift in mood, at least at the beginning, due to the simple fact that they've started. I also wonder (just as an aside) what impact it would have if children and parents were told that they were not allowed to post about any of their treatment online.