Doesn't show that much but I think I succeeded in getting the features of the first little girl's face a little sharper. I selected only the face of the first little since I find it OK that the one at the back be softer.
I went wild on the Unsharp Mask settings with 125% / radius 9.8 / treshold 40.
I found that my increasing the threshold it kept the sharpening on the features but with solfter edges.
Do you notice that it made the white of the eyes whiter and the pupils with more light in them? And I did not play with colors or saturation at all, only the unsharp mask did that.

I tried different colors on your frame, from white to black, but it didn't work. So I simply replaced by a thin black line.