I have to admit, my perspective is informed by building and flying Estes model rockets (the kind with the thin balsa fins and the cardboard tube fuselage). The odds of one of those things surviving landing with all the fins intact is, shall we say, not high, even if your parachute doesn't fail. Of course, those can't be made with the fins penetrating into the fuselage because you need a cavity for the engine to fit into, so it's a little different.

I suppose if you make the fins thick enough (since it doesn't have to fly), they might be durable enough to be through-mounted and still survive a toddler.