I got one this year for my 40th birthday, and I love it!!
Took only a few minutes to get going, and I found it a lot easier than a skateboard. Best thing about them is the carving sensation that you get.
Hint? Put your front foot on first, and don't ride it in the kitchen (crosses fingers hoping wife does not discover large ding in buffet/hutch)

If your kids are really having trouble getting it to work, then do the following on a dead flat and smooth area. A slight uphill is difficult for learners to get forward motion, and even a very slight downhill can be scary for learners and make steering and balance tricky at first.
1. Wear solid sneakers with good grippy soles. This helps you get forward motion working without slipping off.
2. Have them stand on the board while you stand next to them and they can hold your outstretched hands.
3. When they are steady, start to walk along and get them to do the wiggle action that you see on the video that came with it. To get this right, you should not actually wiggle your hips. (doing so will not create any forward motion). Instead, you are working your feet back and forth, as this is what translates power into the board. (although to an observer it does look like you are wiggling your hips)
This should generate forward motion, and once you are moving (even very slowly) it starts to become self balancing. It really is not as difficult to balance these things as it might look.
It may help to think of the front foot as steering the board, while the back foot provides the drive...although once you get used to it, this can change as you learn to do tight turns, tricks, go uphill, etc. Remember, it is how you tip the front of the board (left or right) that makes it steer.
Let us know how you go.
Regards,
Harrow.