Why XKillClient Kills Clients Child?

Question

I'm writting a program on Linux/X that kills the application to which the mouse is pointing.

While it is running I launch xterm and execute "surf duckdcukgo.com &" or "leafpad &". Then I kill xterm with my program using Alt+Escape and both the xterm and the application launched from within it die. Only the xterm should die. If I launch "mupdf some.pdf &" it works as expected. I don't know how the choice of launched application affects the problem. Also sometimes it takes several seconds for "surf" to eventually die.

Is there anything else in addtion to XKillClient that I should do? Should I use something else instead of XKillClient?

Here's the code.

#include <X11/keysym.h>
#include <X11/Xlib.h>

int main(void)
{
    Display     *display;
    XEvent      event;
    Window      root;
    signed int  trash;
    Window      wtrash;
    Window      wfocused = 0;

    display = XOpenDisplay(NULL);
    if(display == NULL)
    {
        return 1;
    }

    root = DefaultRootWindow(display);
    XGrabKey(display, XKeysymToKeycode(display, XK_Escape), Mod1Mask, root, True, GrabModeAsync, GrabModeAsync);

    while(1)
    {
        XNextEvent(display, &event);
        if(event.type == KeyPress)
        {   
            if(event.xkey.keycode == XKeysymToKeycode(display, XK_Escape))
            {
                XQueryPointer(display, root, &wtrash, &wfocused, &trash, &trash, &trash, &trash, (unsigned int*)&trash);
                XKillClient(display, wfocused);
            }
        }
    }
}