Known for his galvanizing park-bench scene in Finding Neverland, in which he redeems a programmatically mawkish denouement with a survivor’s practical pugnacity, British child actor Freddie Highmore beguiles even more in August Rush. Highmore plays the apparently orphaned product of a one-night stand between two musicians (Keri Russell and Jonathan Rhys Meyers) who vanished from his life the day he was born. Now August hears a symphony in every sound of New York City, which he’s combing for signs of his departed parents. Along with a thuddingly uppercase script by Nick Castle and James V. Hart, August’s heightened sensitivity may be one reason why this Dickensian melodrama feels so overexcited in its first hour. Another is that director Kirsten Sheridan, every stylized inch her father Jim Sheridan’s daughter, treats any change in the emotional or climactic temperature as an occasion for poetic cinema. It’s exhausting to watch little August fight his way to freedom and salvation, abetted and hindered by an entertainingly miscast Robin Williams as a bizarre cross between Fagin and Bono in orange hair and earrings, who seizes on August’s musical talent for his own gain. Acclimate yourself to the frenzied vibe, though, and you’ll feel the movie grow into itself as an urban fairy tale whose rapturous finale stakes a wishful claim on the redemptive power of love and art.