Point out that they don’t actually believe that. Like do they think that a kid with epilepsy shouldn’t be allowed to have medicine to prevent seizures? If a kid with severe allergies has an allergic reaction should they just die instead of taking an epipen? If a kid has type 1 diabetes should they be banned from taking insulin (a, gasp, hormone!!) lest it interfere with the natural behaviour of their pancreas? Heck, they probably even support puberty blockers as long as they’re for cis kids. Like if a 5 year old starts menstruating are they gonna say that everything’s fine.
Chances are they don’t actually believe any of this and don’t actually think kids “shouldn’t be on drugs”, they just think trans people are scary and deviant and that our suffering is, at best, not real and at worst believe that we deserve it