Taking advantage of minors and puppets is one issue, yes, along with other "exploits"---such as the one relating to sorrounding a nation's capital and thus cutting off their supply (doesn't work if you're Germany fighting the SU though, for some reason events move the capitals as you advance and sorround them on all sides).
Some people play very, very unfairly---unfortunately, the design of this game itself is typicaly the problem. Like in the aformentioned supply exploit.