Consulting one of my Lego engineers here
……
If the model includes power functions, the motions will either be triggered by a switch or remote – otherwise they’re manual hand- cranks. My boys have had many favorites over the years, however the majority of those are no longer in production (LEGO sets are ever changing). Currently the only power function capable models are in the $100-200 range – yikes. However, if you wanted to add power functions to your 14yo’s current Lego collection, there is a “power functions motor and light pack” you can purchase separately http://shop.lego.com/en-US/LEGO-Power-Functions-Motor-Set-8293 .
For your 10 yo I would recommend starting with something like a helicopter or ATV, as these are good introductions to the building concepts. http://shop.lego.com/en-US/TECHNIC-ByTheme