[Farael]

Ah, but are we not looking at it from the wrong angle?

Wouldn't losing his parents at such an early age make Frodo different from other hobbits, and perhaps more suitable for the bearing of the Ring?

Being orphaned at a young age would make him feel less "attached" to The Shire, being adopted by Bilbo even more so. Being orphaned would probably make him more resilient as well, less prone to asking others to solve his problems and more likely to take matters in his own hands.

Therefore, I'd say that it's not that Frodo was special and so Eru drowned his parents as part of a divine (if convoluted) plan, but rather that this accident, which is nothing more than that, an accident, ultimately made him uniquely able to bear the ring.