Three children are born during a solar eclipse (with an unfortunate conjunction of Saturn, as we will later learn) in the same US small town. This being a horror film and all, this accident of birth turns all three of them into nasty little sociopaths.
A few years later, the trio of kids (Elizabeth Hoy, Billy Jayne, Andy Freeman) begins a friendly murder spree, dispatching of random teenagers on making-out sessions, parents and people they just don't like using shovels, skateboards, pre-Home Alone evil kid handicraft powers and (yawn) a revolver. The police is unable to connect the various murders (and it sure doesn't help that the sheriff who is also one of the kid's parents is one of their first victims), so the nasty little buggers just go on and on killing.
Only Joyce Russel (Lori Lethin) and her little brother Timmy (K.C. Martel) are slowly getting suspicious, but who else would believe these angelic little dears to be brutal killers? The only thing Joyce and Timmy manage is to turn themselves into the evil trio's favourite new victims.
Ed Hunt's Bloody Birthday is a curious example of early 80s horror. Clearly meant as part of the slasher wave, the film's main claim to difference lies in its evil child trio premise. Unfortunately, that part of the movie is rather underdeveloped, with some astrological (yuck) handwaving meant to motivate a rather random killing spree that lacks any deeper connection that would make it more dramatic. Even poor Jason Voorhees has his motives, after all.
A more clever film would be able to turn exactly this randomness of the killings to its advantage; alas, Blood Birthday is not a clever film and just coasts on its not actually very transgressive killer kid transgression.
What's left are a few tight, and many more very very silly murder scenes, not very creepy acting by the child actors, a "dramatic" TV movie-like score that just never shuts up, and José Ferrer and Joe Penny in completely superfluous roles.
I think I'm sounding more nonplussed by the film than I actually am, though. There's just little about Bloody Birthday that provokes any strong reactions in me, be they positive or negative. There are boobs, there is blood, there are evil kids, and all of them are kind of okay.