Much of the dialogue is trite and too much of the acting is predictable over-reaction, probably needing tighter direction, and sharper writing.
Still, remembering the context, 1942 and early days of United States participation in World War II, and bearing in mind young people tend to be much the same from generation to generation -- hormones, peer pressure, unpleasant chores, etc. -- "On the Sunny Side" can be entertaining and interesting.
And, besides, Roddy McDowall is the star, and he is always fun to watch and hear.
Probably the strongest character, though, is played by Stanley Clements, whose characterization was somewhat of a stereotyped bully, but Mr. Clements continued to play similar roles almost to his death.
In fact, he was chosen as replacement for Leo Gorcey in the Bowery Boys movies.
Freddie Mercer plays Don, the young United Statesian who starts out eagerly hosting the young English refugee, but who starts to get jealous as everyone -- except the bully, but including Don's dog -- welcomes the Brit, who becomes quite the big man among Don's family and school mates.
Perhaps it's all predictable, but still, again considering the context, it can be quite a bit of fun, and also quite a bit of sadness as we get reminded of what misery and horror innocent young people suffered because of war.
There is a very talented cast, who are mostly able to overcome the script and directing flaws with their own talent and the basic sense of life of the movie
There is one fight scene that smacks of Yakima Canutt choreography, but not, perhaps, enough, though there are moments of stunt-work genius amidst the bad camera-work and clumsiness.
"On the Sunny Side" was offered On Demand, and I saw it 11 August 2015. It's good enough I can recommend it to anyone who remembers the context.