Funny you waited until now to mention this. You might have mentioned it earlier.
Yes, I run Perl scripts in UTF-8 with BOMs on Windows all the time. It works brilliantly. This is why I recommended it to you in response to your original inquiry: "[H]ow [do I] avoid writing 'use utf8' in every child script…?" Use BOMs instead, that's how. It's the documented way to let the perl interpreter know your script is in the UTF-8 character encoding scheme of Unicode.
If your Unicode Perl scripts don't run on Windows just because they have BOMs in them, then something's wrong. Could it be that you're trying to use Unicode with an ancient and inadequate version of Perl?
Jim