If it's just puberty blockers, as I claim in the previous comment, correct. Which is to say, up to the age of 15, there are no permanent changes. From 15 - the point where they start hormone therapy, that's anywhere between 5-10 years into the overall treatment - there are more permanent changes. The two are distinct phases in their transition.
But nothing really life altering. Will the child end up looking different if they de-transition after taking hormones, yes. More breast tissue if they took E, and more muscle definition if they took T. However, these are also body developments that can also happen without human intervention.
But nothing really life altering. Will the child end up looking different if they de-transition after taking hormones, yes. More breast tissue if they took E, and more muscle definition if they took T. However, these are also body developments that can also happen without human intervention.