Some friends asked for holiday gifts for kids, so I figured I'd post here in case others found it useful.
For the budding electronics hacker: Little Bits are a sure win. MakeyMakey is also a lot of fun allowing ordinary objects to easily be turned into inputs on your computer.
For tactile play and an open API to make your own games (in Python!), check out Sifteo
For crafty building with cardboard and other household materials use Makedo. If you need hardware with more permanence, check out the "Legos for adults" by Makeblock
For early experimenting with robots a Thymio is a good start.
For the aspiring drone operator, a Turnigy quadcopter is a solid low cost solution. But you can also print your own quadcopter chassis and then make your own quadcopter.
Other solid fun is available from the folks at Makie Lab where you can design your own doll. There's also My Robot Nation where you can design your very own toy robot, Mixee Me where you can make your own figure and Figure Prints where you can have your Minecraft designs printed.
And for more fun, go to Fat Brain Toys!