I'm sorry, but what "average life outcome" could be worse than suicide? How could the worst possible "average life outcome" be worse than a child dying?
Keep in mind, this is completely nonmedical intervention. Most importantly, it is completely reversible. If the person changes their mind (if it is a "phase" as most dismissive folks assert that it is), they can go back to their old name and pronouns. If being called by the their preferred name and pronouns will literally save their life, I see that as an infinitesimally tiny price to pay, even if you think it is silly or ridiculous.