function.php blanks out my blog

hello,
I have a blog http://www.vietnamesecinemablog.com

the theme is tiny forge.

I’m trying to edit function.php in my child theme. But everytime I try to download it into my child theme folder (even without doing any editing) it will make my blog blank. Nothing. If I delete the function.php from the child theme then the blog shows up normal.

can anyone advise? thanks