Count me in to the insane group because I also had similar thought when I don't even have a husband yet!
In my opinion piano or keyboard would the best start too. They are easier to play for smaller hands unlike other instruments. When I was little, I started with a very small keyboard which looks more like pianica than a keyboard. I had fun with the rich sounds while learning the basic theories of music. You can move on to more complicated instruments when the kid can handle them better.