In reflecting on the things that sparked my interests as a child, I think it is notable that I can't narrow it down to just one. I seemed to have access to countless creative toys. I remember building a "arctic research station" out of Legos and placing in a snowdrift overnight. I remember the 300 in 1 electronics kit from which I built a radio. Erector sets, Lincoln logs, tinker toys. Some of the things I remember were not toys. My dad's university office held a number of scientific instruments he would let us play with, including one for measuring sound levels in decibels.
If I had to narrow it down to one, it would be the computer. There were a lot of them, starting with the teletype terminal at dad's university where we could play Star Trek on a special account if the system wasn't too busy. And all the craft items we made out of punch cards and program tapes! I wrote about the early computers in my life here.
The latest toy to spark my interest is also a computer. The Raspberry Pi Linux computer is a marvel. It is faster and has more memory than the university's main frame did, yet I bought it for just $35. It can be used for about anything from commanding toy trains via the internet to learning computer system administration. The applications are endless, and the price puts in reach of everyone. I can't wait to see what the toys of my children's childhood bring about!