Mattel Accidentally Puts Porn URL on Back of 'Wicked' Dolls, Apologizes

Mattel's got a "Wicked" big problem on its hands ... 'cause it added a URL to the back of its Elphaba and Glinda toys -- and, it turns out it's a very NSFW site.

Here's the deal ... the toy company's pushing dolls of characters from the movie based on the Broadway musical of the same name -- mainly selling action figures of the two main witches.

On the back of the dolls, they put a URL to the website "www.wicked.com" ... in case people who purchase the toys want to boy more -- except, that's not the company's website. It's a porn site!

Mattel's website for their toy catalog is "www.wickedmovie.com" ... a minor mistake with major consequences for any kid who may have tried the website already.

Obviously, there's a lot of outrage from parents online ... mostly because they accidentally went to the website -- and not so much because their child did.

A rep for Mattel tells TMZ ... they are aware of the misprint -- made primarily on dolls sold in the U.S.A. They deeply regret the error and are taking action to ensure no future dolls have the incorrect URL on the back.

Mattel recommends parents discard the product packaging or obscure the link ... and, anyone with more questions is asked to contact Mattel customer service for more info.

Bottom line ... parents should sharpie out that website on the back of the box -- unless they want to answer some really awkward questions!