Agreed. Java by itself is boring.
At younger ages, pure software is not always that interesting. I'd suggest starting out with a hardware/software mix, like Arduino. Make something cheap with blinking lights that they can take home with them. Buy a few AVRs, a handful of resistors and caps, some LEDs, voltage regulators, and mini breadboards so you can make Arduino clones. If they want to keep them, sell them at cost; it's only a couple days of lunch money.
Once they've outgrown that, move their skills over to the Raspberry Pi and have them blink a LED using Java or Python. Now, they're on a cheap, fully functional (albeit a bit underpowered) Linux system. They can learn BASH, Python, C/C++, etc. by seeing and tweaking what's already there. And if they break it, you're only out $35. Or if they want to continue playing at home, they're only out $35 plus accessories.