I didn't find this particularly sexy - she's a child. My kids used to love to put on makeup and play dressup and, yes, sometimes straps of sleeveless tops would slip down as they ran around. There was no intent to be "sexy".
But, this does remind me of a funny story. My 4 YO had a bright pink bathing suit. She went up & stood at the end of the diving board to jump down to the waiting arms of her swimming instructor. Until she went into the water and got the suit wet, we had no idea that it would make the suit stretch. So, there she was, for all the world to see, with the stretched straps and her bathing suit all scrunched up down around her waist! Fortunately, she was only four so everone thought it was cute and funny. But she still gets teased about this today.
And in all likelihood, you made your children wash their makeup off when they finished playing because it was all over their face. In HaLeigh's case, Misty did a hair and makeup routine on HaLeigh before she left for school on most days, and obviously the results Misty achieved had the power to transform HaLeigh to look much older than her true age. HaLeigh's community is infested with SO including members of Misty's family who allegedly molested young girls and I'm surprised HaLeigh's teacher was okay with this.