Translation:His mask is too scary for little children.
No, you can't. "Petits enfants" indeed means both "grand children" and "small/little children", but its English translation depends on context.
Basically the only moment "petits enfants" means "grand children" is when a grandmother or grandfather themselves refer to their own grand children. Otherwise "petits enfants" always means "little children" (small in size).
Hi Paul, you are right but I think if you needed to make the distinction you would change 'les' for 'nos ' i.e. our grandchildren. In this case upon reflection it would mean any old little kids! Think I tried putting grand children in once and of course it wasn't accepted. Stay safe...