Yes Peter you are correct Gustav Genschow did make some double rifles.I am lucky enough to have a 500 X 3 1/4" Nitro for Black made in 1927 Boxlock non eject in the clamshell style of action.My first double rifle. The bore size is not quite as big as yours but the weight of mine is nearly twice as heavy.
I hope your kids enjoy what looks like a great little gun

good shooting
sbs470