Try WD40 or similar on the lock mechanism and hinge. Apply it with a generous hand, and let it soak in for a few minutes, then try again. If it's just jammed, that may be enough to get it moving again.
Hit the lock sharply a few times, though obviously be careful not to use enough force to damage your case. It's not the best way to unstick a lock, but it could be just enough to loosen the mechanism, so it's worth a shot.
Worst case scenario: cut the lock hinge. You're going to need really heavy cutters, if not actual lock cutters (you can find those at hardware stores). If you're careful, you'll still have a box to store your toys in, though it won't latch closed anymore.
Good luck, and I hope you manage to get your toys out soon!