Disrupted misfire

Hi guys, this is my first post so go easy on me😁. I bought my kids a disrupted each for Christmas, so they're probably 2 weeks old or so. They didn't have the strength to cock them so the guns haven't had much use. I've had to replace the first one as it sounded like the chamber was leaking when it was cocked (a kind of ducking noise) and half the darts either didn't fire, or had a vastly reduced range. The 2nd gun has now had the same issue, being that neither has had much use, an I abusing them, or is there a critical thing that I'm missing?

Cheers