Samsung has already rolled out Android 4.4 KitKat firmware to the Galaxy S4 (both I9500 and I9505 versions). It included new TouchWiz goodies we've seen before in the Galaxy Note 3, but it was lacking a few things like Kids Mode and KNOX 2.0. As it turns out, though, Samsung isn't done with the TouchWiz updates, as it has just seeded a new firmware improving on the TouchWiz UI.
The new firmware weighs about 130MB and is available both via the Kies desktop software and OTA. It will add Kids Mode on your Galaxy S4 plus the latest KNOX 2.0 security package - both features that Samsung premiered on the Galaxy S5. The update also improves the power management and will extend your battery life, plus it squashes some bugs and brings minor improvements to the performance and the user interface.
Currently the update is available for the I9505 Galaxy S4 model in Germany, but we bet it will spread to other markets and models soon. If you discover even more new features coming with this update, feel free to share your experience in our comments.