Play video content EXCLUSIVE TMZ.com

Brandi Glanville went into fierce mom mode after running into a fan who brought a little kid with her to score autographs at night ... and her scolding is hilarious.

We got the ex-'Real Housewives of Beverly Hills' star leaving Catch LA Tuesday around 9:40 pm where she bumped into a lady who had a child with her ... which was not okay with Brandi.

The autograph-seeking fan offers an explanation as to why the tyke's out so late, but Brandi wasn't really having it -- especially as a mom of 2 boys herself.