Assuming it is, in fact, a firearm (or was at one point) I think it interesting that the grip appears to have been solid metal, as opposed to cut out. Also, the grip shape looks more modern than anything I've seen on a pinfire. That said, the overall design is vaguely that of a Lefaucheux, with a drop-down trigger.
One other possibility is a much more modern toy revolver of some manner. Which would explain the apparently entirely metal construction, yet seeming inconsistent proportions - cylinder, barrel length, grip, etc.