I think the number of people who will copy-paste from a website and not revisit it may be alarming. It is on those who publish snippets to make these things explicit. Maybe the following is enough:

    if (pid < 0) { /* TODO: handle error */ }

Reading the actual code I doubt it's just an oversight, the coding style used seems to lend strongly towards not thinking an error is possible:

    if ((pid = fork()) == 0)
    { //Child
        longTask(); 
    } else {
        children[i] = pid;
    }