Kol Isha (3)

Sometimes a quick exchange communicates more effectively, and more personally, than an article. Sometimes, just seeing that others share our questions can make us feel more connected. Our posted questions and answers are an opportunity to learn from each other. Keep in mind that each questioner’s situation may be unique, in ways that affect the halachah. Even the tone of a question can affect the tone of an answer.
How does kol isha work with chinuch? For example, if I am davening/ bentching with my children and e.g. my father in law is present. Or running children services in shul with men present.
There's a video of me singing that I'd like to post on youtube. I'm dressed tzanua but singing solo. Is it okay for me to post it publicly? Do I need to add a warning label saying that it's kol ishah?
When a wife is in her yemi nidda, is there a restriction of Kol Isha? Thank you!