Update: the 3 year old managed to destroy the door on the front he loved the glowing lights of the fan controller) . I could not salvage the mobo tray (did save the HDD cage for a little while, but thats gone now too I think.
It was my nephew, not my son, so no spankin' followed by an explanation of what the thing is, which despite having 3 children can't seem to speak normally to a child, so the eyes glaze over and he would be so bored would never want to touch it again, cuz it would make him think about my lecture on electricity and voltage controls (vice PWM control) and he would find something to break instead that was not explained to him. My son is a demolition expert too, but I took the time to raise him right and he understands PCs now, especially the fragility of cases you get on ebay for $50 shipped
(In truth I do not spank, not after 2 years old. The threat of it is enough, talking does the job, only when I have to repeat myself do I use corporeal punishment)