You have nothing to be concerned about, for multiple reasons.
First, even if your friend's husband has it, it doesn't necessarily mean that she does. It is definitely possible that your friend became pregnant without catching HIV.
Second, your friend would have been tested for HIV routinely during the course of her pregnancy. In the event she tested positive she would have been put on antivirals to reduce the risk of mother to child transmission. Thus, it is unlikely your friend's playmate even has HIV. Another way to look at this- there were only 139 HIV/AIDS cases in children resulting from perinatal exposure in 2007, out of tens of millions of children.
Third and perhaps most importantly, transmission between children has never been shown to occur, even though kids often get into fights/scraps that result in open wounds. As you stated, the virus doesn't spread by casual contact- it requires direct inoculation inside the body for transmission to occur.
When all of this is factored in, the chance that your daughter could catch HIV from this boy is effectively zero.
My advice- turn your attention to more realistic concerns, such as the upcoming flu season, and forget about HIV.
HIV is not spread through casual contact , this is no cause for concern and there is no need to worry. best wishes erin