Just to be clear chest binding and chest ironing aren't the same thing.
One is mutilating someone else's chest with heavy or hot objects, damaging the breast tissue permanently. The other is wrapping your own chest with soft material to reduce the appearance of the breasts. It causes no more physical harm than wearing sports bras - in fact, it causes less harm by distributing the weight more evenly across the back.
Breast ironing is: “the process during which young pubescent girls’ breasts are ironed, massaged, flattened and/or pounded down over a period of time (sometimes years) in order for the breasts to disappear or delay the development of the breasts entirely...large stones, a hammer or spatula that have been heated over scorching coals can be used to compress the breast tissue."
Chest binding is: "the flattening of breasts with constrictive materials such as cloth strips, purpose-built undergarments, often using spandex or other synthetic fiber, and shirts layered from tight to loose...Binders may also be used as alternatives to bras or for reasons of propriety."
Children and trans issues are an entirely separate discussion point but being outraged by your own confusion doesn't help real issues by discussed. Trans people are not engaging in chest ironing.