Adult Mitzi Trumbo?

How weird they don't credit the actress.

I read Steve Martin's book, "Born Standing Up" and if memory serves, he dated Mitzi Trumbo in his young days. He didn't really know who her dad was at that time, but went to their house for dinner and says it was the first time he was ever around adults who used profanity in front of "youngsters". That was such a great book.

I haven't seen the "Trumbo" yet but really want to.

I think you refer nikola (niki) trumbo. OP asked for her little sister mitzi trumbo.

I've seen almost any movie Elle Fanning ever appeared in, would never not recognize her ;) See reply of yangz.

EDIT:
However, thanks for clarifying the following: "If you mean the 1970 scene near the end where Trumbo addressed a group and his wife, son, and daughter are in the audience, ..."

You were right there, except for "daughters", not "daughter". That's the point. As said in the original post, I'm looking for the uncredited one. She looks familiar to me, so I'm wondering why no one submitted an uncredited entry so far.

Becca Nicole Preston was about 11 when filming Trumbo.

Here's a picture from another set, same time period:
http://www.imdb.com/media/rm3878143744/nm6734378
And here's another one from the set of Trumbo itself:
http://www.imdb.com/media/rm534766336/nm6734378

Also, as you said yourself: "... Mitzi Trumbo (age 9-12)"

Now how does that comply with the subject "Adult Mitzi Trumbo" 