"A woman with two children believes she has three and her husband and oldest daughter play along with her to keep her balanced (or as close to balanced that a woman with an invisible child can be). However, when the family hires a new nanny, it is all just too much for her and she starts to blab." IMDb plot summary.

https://www.youtube.com/watch?v=PQvO_93voio
https://www.imdb.com/title/tt0172606/reference