The piece is really adorable, however I feel that there are some things that could be improved, the main one being the proportions. I feel like part of their legs are missing and that you could either make the legs longer (or make them appear to be sitting or something would would make the legs seem less out of proportion) or make the torso and arms shorter in order to get everything in proportion. Otherwise I think this piece is absolutely precious and feel that other than the issues with the proportions of the legs to the rest of the body that it's great.
Yes, keep it. I don't usually like anthropomorphic ponies, but these here are quite nice. You didn't overdo them or anything and successfully restrained yourself from adding unnecessary anatomical details. They are chibis after all.
Will you draw them just occasionally when you feel like it or will there be a series of some sort?