An article that came up in my news page today quoted Dr. Suzanne Kavic, director of the division of reproductive endocrinology at Loyola University Health System as saying that "...the heat generated from laptops can impact sperm production and development making it difficult to conceive down the road."
Since they didn't quote any research that backed that, I went to check it out. I found this abstract from Human Reproduction where Yefim Sheynkin, Michael Jung, Peter Yoo, David Schulsinger and Eugene Komaroff tested men for scrotal hyperthermia when working on laptops.
They tested 29 volunteers and found that indeed the use of laptops raised the temperature between 2.6-2.8 degrees celsius. Based on the abstract, "scrotal hyperthermia has been identified as a risk factor for male infertility" - so they've shown that laptop computers cause scrotal hyperthermia and since that's a known risk factor for male infertility, it definitely sounds like something even young boys should be made aware of.
I see there are already patent applications and products to help solve this problem.