(There is no sexual intention behind this picture at all. It's kind of on the age, but no sexual content implies here. The breastfeeding is for nutritional purposes. It's borderline but that's it)

A mother mare is laying on the ground feeding her foal when she noticed much older mares dressed in foalish clothing doing a similar thing. Except, Starshine Twinkle is clearly in lactation and her udders are full (Yes, horses have utters, but it's different from cattle, they're called teats also), and it looks it was too uncomfortable for her so she removed her diaper and sat down, forcing Shatter to nurse, more than aware of an actual mother and foal nearby but she got no choice. It just happened that when Shatter was nursing from Star, her diaper shows from underneath the dress, unlike Star, Shatter was intending on hiding the diaper to avoid mocking from other ponies, but luckily where they're at, there isn't any pony they know so there will be no blackmail.