I agree that it sounds uncomfortable for a child to make just a permanent life-changing decision like that, but the counter point is that transitioning is significantly easier on the body and mind before puberty happens.
In the vein of 'do no harm', I'd tend towards delaying it, even though it might be harder later, rather than proactively pushing a treatment that will later be revealed to be a mistake. It's too hard to present the options to a child without putting bias and pressure on them.
There are some exceptions to these rules, of course. One in particular is athletes. Society happily will fundamentally alter a child's or adolescent's body in pursuit of athletics.