She shouldn't be able to keep the other kitten either! First of all a Toddler should not be left alone with a kitten. If she was supervising them, it probably wouldn't have happened. And, quite honestly, I don't see what the big deal is. Kids get bumped, bruised and scratched all the time, one little scratch is no reason to abandon a helpless kitten alone in a park.
I sure hope her toddler doesn't go through a biting or hitting stage like many do...what would she do then? Bring her child to the same park?
Do you know where she did this? What town? What park? Maybe one of us lives locally?