Methinks you're confusing this somewhat with Gulliver's Travels. Jack in Jack the Giant Slayer is Nicholas Hoult, a decidedly different [and British] actor.
Well, sort of. The JACK THE GIANT SLAYER name is similar but the plot line and characters are completely different, and to my mind, not nearly as good as in the 1961 edition. Granted, the original has some crude effects work, but Kerwin Mathews fits the role better than Jack Black (just as few actors would have worked as well as Black did in SCHOOL OF ROCK). And Judi Meredith was simply a babe, even as a witch. Plus there is the bonus of Torin Thatcher, bringing the film a little closer to being a 7th VOYAGE OF SINBAD rip while never quite being one. Nice Paul Sawtell / Bert Shefter score (available on CD).