I'm pretty much ok with the system you appeared to have went with, which is wait for hard-core amphetamine use until they're an adult and able to decide for themselves the cost benefit analysis.

These kind of questions regarding the benefits of kids can be exceedingly difficult to answer. From a moral perspective, like you I take the hardcore an-cap kind of viewpoint that the family has the right to inject hard drugs for fulfilling what they view as industrial output needed for survival. Ultimately perhaps we have to trust the parent is making the best choice for their own family and try to defer to the family in this kind of gray area. Personally I would never give my kid amphetamines unless it was unambiguously life and death like they were unable to perform day to day activities without it.