Risks of medical intervention always should be weighed against risks of nonintervention.
If there is a significant probability a child is trans, delaying puberty may be the least intrusive option. There is a chance of negative effects, like with all medical interventions, but if they are most likely trans forcing them to undergo puberty is much more likely to have long term negative effects (including suicidality).
Why is this specific medical decision equivalent to kids having sex? Do you view other procedures, like deciding to have braces, the same way? What about much riskier treatments with a muddled short/long term prognosis, like some heart surgeries?