Is this possible?

[lugerholsterrepair]

Till, The Luger is actually a striker fired weapon. The fireing pin is moved to it's backward position, compressing the fireing pin spring and latching on the sear. This could remain for many years but would leave the spring compressed. The spring MIGHT develop a slight weakness from compression for 40 years.
In your scenario, the child would only need to slip the safety lever to the proper position or if it was already on fire, to pull the trigger.
Most, not all WW2 German Lugers had no magazine safe. Police Lugers MIGHT have had a magazine safe installed although it was far from the norm by the end of WW2.
I would say an 8 year old boy, not girl..could pull back the toggle on a Luger but here's a potential problem. If the toggle is not let go of but held and slid into position it is possible for the bolt to decide not to fully seat. This will leave the bolt out of battery and the pistol might not fire unless the shooter recognizes the toggle bent up and slaps it down and into position.
Antique ammunition can present some problems. The primer might fail altogether. Often he mercury and other primer componants will degrade and you get a failure to ignite the powder, this might push the bullet midway down the barrel simply by the power of the primer alone. Sometimes the powder has degraded and it will have less power than originally.The round will fire but it is a squib load..Pushing the bullet out but with much less velocity. The scenarios can continue..The powder can degrade into smaller pieces than original manufacture causing it to burn faster than intended and a much more powerfull detonation occours.
Brass degrades over time..a crack could develop in a brass cartridge case and apon fireing it could cause gas seepage into the bolt face and regions behind and blow magazine out and the pistol up.
I guess I could think of another scenario or two but this might do it...

Jerry Burney