Puberty blockers are not "irreversible." Kids take them under medical supervision and if the kids decide they're not TG, they just stop taking them and puberty proceeds. However, if they ARE transgender, this gives them an opportunity to avoid a puberty that would be distressing for them and allows them a chance to express the gender they experience. Surgery performed in accordance with the "standards of care" for transgender people would only happen when the patient is old enough to give consent (so no kids) and their medical team (including mental health professionals) agree that it is appropriate. This stuff really isn't as unsupervised as many seem to think.