Hi!
As has been said earlier our glow engines are made of aluminium and thus doesn´t rust. The only thing inside the engine that can rust and often do so, is the bearings, crank and piston pin. Of these three the bearings is often the culprit. The carb barrel is made of steel too but it's not likely to rust, especially after just a few days outside.

What does make a engine freese up is old congeled Castor oil, and this is easily fixed by heating the engine with either a propane tortch or a heat gun.
But...in my opinion, take the engine apart and clean it! If you cannot turn the crank over the ball bearings certainly needs a looking over and probably need to be changed.