This function returns the handle of the child window with the specified identity.

#define INCL_WINWINDOWMGR /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HWND     hwndParent;  /*  Parent-window handle. */
ULONG    id;          /*  Identity of the child window. */
HWND     hwnd;        /*  Window handle. */

hwnd = WinWindowFromID(hwndParent, id);