I remember watching an English language (probably live-action) film as a kid (on the TV, but I don't think it was a series) about which I remember the part where there was a group of people who could turn invisible when they held their breath and, at one point, they are almost given away while hiding when one (possibly a child) can't hold thier breath long enough. They were possibly aliens. This would have been early 80s, I think, but possibly an older movie being reshown. What movie was it?
Based on the holding-one's-breath-to-turn-invisible plot device, the time-period, and the match of many other descriptions you gave, I'm guessing this is the film you are looking for.
In the comments for this video, someone posted: