@Landsteiner posted:"I'd find 'em an older MTH (I have an AT&SF engine with a 605 tender) that smokes great"
I wouldn't be exposing a child to large amounts of vaporized hydrocarbons (mineral oil). Not ideal for the lungs to be sure. Just some free advice from someone who knows a thing or two about lungs .
I suspect there are a host of things a child will be exposed to that are far more dangerous than a little model train smoke!