"I look at the listings and I think well OK, so there are some wonderful animations," Thompson said. "But as for live action movies, there are very few really good ones for children that aren't just a series of very quick cuts that make me want to... that give me motion sickness."
So she got busy writing a new story centered around a new family for Nanny McPhee to help, one that features lots of laughs, but a few tears just may sneak up on you, too.
"I've watched a lot of audiences and it's very funny seeing adults particularly doing that kind of [crying], and it makes me cry too," said Thompson.
The part of the process that really brought tears to Thompson's eyes was sitting for hours in the make-up chair while she transformed into the tough-as-nails nanny with a heart of gold.
"I never multitask before 6 a.m. No, I just sit there while my poor and sainted make-up artists work on me," said Thompson. "It is a science, you know, they've got it down, by the end of this shoot, to an hour and 15 minutes, which is not long. It's quite demanding, but every time I get into it I think, well at least I'm not playing a Klingon."
The PG-rated film opens in theaters on Friday, August 19.