The O.C. Wiki
The O.C. Wiki

Princess Sparkle is Summer Roberts toy horse, is an object to which she is really fond of.

Story of the "object"[]

As is Captain Oats, for her boyfriend Seth, Princess Sparkle, is an important item for Summer, we don't know much about how Summer get the toy horse, but we know that she cares about the object, at least for the first three seasons. We don't know much about the toy after the third season.