C++ Kill child processes, but not parent, and uptime through exec function

I don't know if the current way I am killing the child processes is correct. I want when child three's timer (temp) hit's zero that it kills all the children, then the parent prints a message than exits. Also, I tried using sysinfo to get the uptime in child 2, but the sysinfo struct doesn't have uptime as a member in the environment I am running the program in. So, how do I use a exec function to get uptime from /usr/bin/uptime. Also, don't tell me to split everything up out of the main function because I am going to do that after I figure out how to complete the functionality.I don't know if the current way I am killing th