If steroids would be a net positive for the body in general, then evolution would just follow the gradient and produce more of it.
> if steroids are indeed a net positive for the body they might even have legal choices available by the time they're adults
That's a huge "if ... might" there. Again, what are you telling your children? That gambling with your health is ok?
Think about teeth for an obvious example: The body is able to grow them, and some animals do it constantly - yet losing our adult teeth (due to aging, accidents or whatever else) does not cause us to grow new ones. It would be hard to dispute that growing a replacement tooth would be beneficial to a person in our current context and lifestyle, but evolution has not reached that conclusion.
Edit: Replying also to your second phrase (the message I'd be giving to my potential children) - I don't really see why, if current research points to minimal to no dangers for short term use (about as harmful as light alcohol consumption), I should be treating it as such a big deal. If anything, I think it would be a positive lesson that they should make adult choices for themselves by taking appropriate steps to be informed about the pros and cons of it.