I couldn't get the video to play in the Op, but I went and found the trailer myself elsewhere.
First of all, I see this as a much more realistic portrayal of what girls actually go through growing up, a huge improvement from some fake iCarly BS that no one actually experiences. Second, girls have been wearing bikinis, tank tops, short shorts, mini skirts and leotards since we were toddlers, and it is beyond irritating to me to constantly having people police what girls "should and should not wear". When I view the poster above, I do not see it as "sexualizing" young girls as much as I see it "empowering" them to feel confident in their own skin. When I was in gymnastics, dance, cheer and ballet, i wore skimpy outfits, but I certainly did not want any more clothing on me while I performed, it just gets in the way. The world constantly trying to act like a girls body should be hidden is seriously messed up tbh and does more harm to young girls than just letting them wear what they choose to wear. We do not need to have the modesty police attack us when we are 4 or when we are 25. I for one do not regret jumping out of my bathtub and running down the street butt arsed naked as a kid and no one should be forced to feel bad because other people can't help but be so judgmental and impose their own level of modesty onto everyone else. It is bad enough they slut shame women, slut shaming girls for wearing dance gear is even worse. Girls should be able to wear what they want. What some dude thinks about what they wear is his problem, not hers.
Growing up in the Bible belt in the US, a lot of this hits home. Girls are constantly receiving mixed messages about who they are and what everyone else expects them to be. My brother's girlfriends parents tried to send her out of state and marry her off at the age of 14 to some old man, my brother literally hid her at my parents home to stop it from happening when he was 13 and this is the wealthiest per sq ft county in the state of Texas, not some land far away... this crap is still happening in the US: