'Harry Potter' Star Miriam Margolyes Says Adult Fans Need to Grow Up

Miriam Margolyes says people who are still diehard 'Harry Potter' fans as fully functioning adults worry her a bit -- and she's got a clear message for them ... grow the hell up!

The actress -- who played Professor Pomona Sprout on two 'HP' films back when those were still a thing -- did a recent interview with New Zealand's 1 News, where she was plugging a new project of hers ... and she was quite candid on how she feels about this topic.

Check it out ... Miriam says people that are still obsessed with the 'Harry Potter' movies -- or, god forbid, the even older books -- concern her ... 'cause they're still acting like lil' kids.

She says she'll still get asked about 'Harry Potter' stuff to this day -- and goes on to say she's startled to hear people are doing whole ass 'HP'-themed events ... including weddings. Miriam jokes that she wonders what the first night of fun would be for 'HP' newlyweds.

As Miriam puts it, 'Harry Potter' is for children, and the adults still clinging to their childhood nostalgia need to get over it. MM hits the point home by definitively saying ... "It's over!"

Yes, it's a bit harsh -- but you can tell Miriam just doesn't understand the years-long fandom.