ZD,
Halachakly speaking, (i’m not speaking from a chinuch perspective) watching your iPad is no doubt the better option. Smoking is deOraysa on each and every puff, plus igniting the fire (and who knows what other issurim that “hanging out” will end up with), whereas, iPad usage might only be a Rabanon.
On the same note, perhaps you can request/explain the OTD child that you understand you have issues and you can not be restricted to keep Shabbos, but if he can please do you the favor and only transgress Issur Rabanon’s (Muktzah, only using a train Uber, bus, etc, only led lights etc.).
Does anyone suggest the above?