The group of parents who let their kids smoke might get those instead, improving their health
The parents who don't allow it would never consider them
I suppose it depends how many of group 2 could be converted to 1 if they were "low tar!".. my intuition is close to zero
Group A is going to smoke regardless, having a healthier product reduces harm
Group B is never going to smoke no matter what's on offer
If we instead imagine a world where parents allowed, even encouraged 60% of children to smoke, and there was no clear route to outright stopping them, giving them at least a better alternative that doesn't hurt them as much would be worth considering
I think it's still better to ban these obviously harmful things and to reduce exposure to them as much as possible.