Electronics
Electronics seems to me to be more fun as a hobby than it used to be. Back in the 70's-80's you had to build everything from scratch, so you had to spend a lot of time crawling before you could walk. Now there are a lot of black boxes available. Need an ultrasonic ranger? Black box. A micro-controller? Black box. LED array controller? Ethernet interface? Video controller? Scrolling LCD display? All black boxen. I still remember having to build a LED array controller from scratch, that was a project in itself. With all the hassles, I eventually gave up--when you spend all your time building the boxes you never get to the interesting projects. In some sense, maybe I learned more, but in the end it is not a good trade. Sometimes learning less detail and achieving bigger projects is better--with those sorts of successes behind you, you are much more likely to stick with it. Building voltage dividers, hand wiring LEDs to transistors to control their blinking, and getting a 7-segment LED to show the number 8 are all achievements, but boring ones.
On top of all that, there is the internet with a lot of information, more electronics manufacturers than back then, cheaper components, plentiful micro-controllers (often at $30 or less when buying them individually), and a much larger community of people interested in electronics. This community is more diverse, too. Back in the 70's it was all late-night tinkering by electrical engineers building devices for model trains and airplanes, or just building gadgets that looked cool from a technical perspective. Now there are so-called makers looking to control things they make, artists building interactive art, and people sick of waiting for obvious problems to be solved by someone else.
Kids not playing with all this junk today had better be doing something else creative. There are just fewer and fewer excuses every passing day.