FAQ

Answer: It was a retcon made by screenwriters Ed Solomon and Chris Matheson. Solomon explained it in an interview for Cinema Blend website: ''I'd like to pretend they were always girls. They weren't always girls. We assumed, because we were adolescent boys when we wrote Bill & Ted's Excellent Adventure (1989), and we were barely post-adolescent boys when we wrote Bill & Ted's Bogus Journey (1991), of course we assumed they were going to be boys. They happened to be played by girls, interestingly. Candace Mead and Lauren Mead played those characters. But regardless, look, we were immature adolescent males. And so we wrote an immature adolescent male fantasy. 30 years pass. Life changes. The world changes. We change, we grow up, we get married, we have children, we have sons, we have daughters. And of course our culture evolves, as it should. But we still, in 2009 and 2010, we thought, 'Let's write them as boys.' Because that's what we figured! Young Will and Theo. And I cannot tell you how boring they work. Oh God derivative. Stale. We tried to give them like Bill and Ted type voices. Just unbelievably like rehashed crap. We hated it. We tried to make them into cool guys. That was stupid. And then when we finally had the idea a few years later, 'Wait, why are we beating our heads against the wall with this? What if they had daughters? What if it's Billie and Thea?' It just opened it up completely. So that's much better idea. And it helped us with something we were trying and to do anyway with the movie, which is -- the first two movies, they are male centric. They were written by boys who knew no better. And so this also gave us a chance to go, 'Let's just widen it, man. Let's like, let there be more of a female presence and just make it more inclusive'.''

In 'Face The Music', a short exchange early on in the movie directly addresses the issue:

Captain Logan: Be role models to your daughters.[...] You remember when you used to call them, 'Little Bill', 'Little Ted'? Billie: We thought it was cute, Gramps.