Story goes that she "lied" about her age.

http://www.kidzworld.com/article/23157-mila-kunis-biography (there are other sources for this as well: Did you know that Mila had to lie about her age to nab the role of Jackie Burkhart? The producers of That 70s Show were looking for an 18 year old actress, but Mila was only 14! Nevertheless, her charm and sneaky answer (Mila said she’d be 18 “on her birthday,” but she didn’t say which birthday!) had cemented her in the role of Jackie.)

Surely since they are only making a small decision like hiring a lead actress for their major network sitcom they would not have bothered to check her resume. Because had they done that they would have found out that she had just prior been playing a young teenager (obvious one at that) in the TV episodes 7th heaven.

Clips from her on the show: https://www.youtube.com/watch?v=3qsDv9HS5F4

They began airing in 1996, That seventies show premiered in 1998.

In 1995 she looked this young in Baywatch:

http://www.imdb.com/title/tt0394233/mediaviewer/rm3810867456

Still didn't stop the creators of That 70's show from casting her as their main star and having her act out scenes like this, when Jackie is about to lose her virginity:

https://www.youtube.com/watch?v=ioWUuQyaatM

And she is obviously being fetishised throughout most of the series, I'm not sure from which seasons these clips are but you get the idea: https://www.youtube.com/watch?v=RydtgecDMGg

Watching the clips from 7th heaven gave me a weird vibe. Here they are seemingly taking a stand against this kind of thing so there is nothing really wrong about it that you can put your finger on... https://www.youtube.com/watch?v=DoJaQ2ebBKo but maybe it is this skeptical mindset after researching this topic, to be skeptical about a show revolving around so many teenagers coming from Hollywood. Maybe it is the fact that the name is in part a reference to "7 minutes in heaven" which we all know has some suggestions that imply that there might be some sexual themes in the show. Whatever the reason my hunch was proven to be on point pretty quickly since well... The main actor in the show has admitted to molesting children that were on the show:

In case you need further proof than the Daily Mail ... well, here is an audio recording of his confession:

https://www.youtube.com/watch?v=Sy1a7DM6GXs And his interview about it: https://www.youtube.com/watch?v=h4g1dTDcOM0

http://i.dailymail.co.uk/i/pix/2015/03/09/267A2C8300000578-2986695-image-a-45_1425929954065.jpg

This is a picture of his victim. Here she is talking about it recently: https://www.youtube.com/watch?v=2MpVSpNwMWg

It does not seem plausible that a guy who is an admitted pedophile that acted in 243 episodes over the span of 9 years with young teenage girls only had a few incidents of "indecent exposure". This smells a lot more like a Savile situation. You would think that a pretty girl like Mila Kunis, also acting in the show would have been in immediate danger working this closely with a person who has a sexual attraction to kids and has admitted to acting upon those urges, keeping in mind that he only admitted to it after being accused and does so in a manner that is downplaying his crimes and did not mean to do so publicly.

Then of course there is her husband doing this:

https://www.youtube.com/watch?v=nJJh5bp7G7w

And heads an organization fighting human trafficking.

This is speculation at this point but I feel like there is plenty of circumstantial evidence and I would be surprised if Mila was not harmed during this time by the many vicious pedophiles hovering around Hollywood. I hope she wasn't but at this point it seems like there is a lot of smoke.