Want your kids to learn physics? Throw away the computer simulations. Build things with them. Run experiments. Observe and think about the results.
To teach physics, start with things like C-clamps, string, rubber bands, wire, springs, low-friction carts, compasses, magnets, thermometers, balloons, weights, scales, and pulleys.
More advanced stuff: a voltmeter/ammeter (analog stuff), an old oscilloscope, an air table (a kids' hockey table), vacuum pump & bell jar, countdown timer/photogate, etc. Many of these things show up on craigslist for cheap (I picked up two free oscilloscopes and have given them to my sharp high school students).
Computer simulations? Naw. Have your kids do real physics:
A pendulum made of a bowling ball and rope. Time the pendulum swings and then ask: which will change the period - changing the lenghth of the swings, changing the weight, or changing the length of the rope?
Fool around with a signal generator, an oscilloscope, and a microphone. What's a sound wave look like? How is frequency related to period?
Play with thermometers, ice, water, and fire. What's the temperature of ice and water? Can you get water colder than this? How hot is water from the kettle? Can you get water hotter than this?
Get a voltmeter, wire, and some magnets. Can you really induce a voltage by moving a magnet nearby?
Don't sidetrack your kids with simulations & computer graphics. Real physics starts by fooling around with reality.
Obs Feynman quote: "It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong."