I think I just put my finger on what it is that makes me uncomfortable about this.
First of all, Bratz are supposed to be early high-schoolers; say, 13 or 14. At 13 or 14, it’s generally considered to be age-appropriate to begin to use a little makeup for special circumstances, and to dress a bit more like an adult than like a little girl. (Note that “adult” doesn’t have to mean “sexy” per se, but yes, women’s clothes are generally designed with the adult female form in mind–as they should be.) However, 13/14-year-olds are also still very much children, so taking off the Bratz dolls’ makeup and making them look like cute little girls swinging on swings and the lot is at least age-appropriate.
Barbies, however, are a separate issue. While I wasn’t ever into Barbies (my parents didn’t allow me to own them), they’re fashion dolls. It’s generally implied that Barbies is a late teenager/woman in her early 20s, if judging only by her career and life options (wedding, doctor, etc). It’s far more appropriate for a, say, 18-20-year-old to wear high fashion dresses and very, well, womanly clothes, than it is for a 13/14-year-old girl. And that’s what makes me uncomfortable: doing this to Barbie would essentially remove her “womanliness,” and is reminiscent of those movements which say that women mustn’t wear any makeup or attractive clothes lest they cause men temptation.
Finally, however, I went back and looked at the video, and I did do a disservice to the people who had this idea. They were only using Bratz dolls for this demonstration, not Barbies. I still maintain that there’s nothing wrong with girls wanting to play with fashion dolls who wear beautiful dresses and the like, but Bratz don’t really have that culture around them. I do still think it’s a very interesting idea from an arts-and-crafts perspective, and it’s certainly cued me to think about the whole thing a bit more.