That's a huge leap in logic to assume that certain companies funding of research investigating global warming claims constitutes outright lying.  While the scientific consensus has come around to indicate that there is some affect of human activity on climate change, reputable scientists will allow that there are a number of factors that may cause such changes, and some of the alternative research goes into that. 

While it may be convenient to label those who fund such research (when it could benefit them) liars, I think it is intellectually dishonest to do so. 

Further, your son's question about national leaders investing in energy companies is based on what?  Cheney worked for Halliburton, who is not an energy company but rather a supply and technological assistance firm.  Hell, anyone with a 401k probably has extensive investments in the oil sector. 

I wouldn't put it past our "leaders" to make their own conclusions (or policies) in a way that is colored by the bias of their experiences or financial interest.  But to label them liars on the back of the global warming issue trivializes the real decisions it may necessitate. 

Of course, many people still believe that had the United States supported the Kyoto Protocol, greenhouse gas emissions would actually have gone down.  In reality, support for the Protocol would have amounted to a massive technology giveaway to non-signee nations such as India and China, who will soon account for the lion's share of emissions anyway. 

None of this is to say that we ought not to care for emissions or even pass laws to lower them.  

You've hit on a pet peeve topic of mine.  It reminds me of my college days when the English majors would weigh in on environmental issues without any understanding of the science (or statistics!) involved in their arguments.