Why is $$ returning the same id as the parent process?

You can use one of the following.

• $! is the PID of the last backgrounded process.
• kill -0 $PID checks whether it's still running.
• $$ is the PID of the current shell.

$$ is defined to return the process ID of the parent in a subshell; from the man page under "Special Parameters":

$ Expands to the process ID of the shell. In a () subshell, it expands to the process ID of the current shell, not the subshell.

In bash 4, you can get the process ID of the child with BASHPID.

~ $ echo $$
17601
~ $ ( echo $$; echo $BASHPID )
17601
17634