It is a really tough one that. we have similar *issues* when we take DD to play in the park. she is quite small for her age and has had to bear the brunt of some toddler thuggery lol! I usually in a firm voice to the child in question (as i am picking my child up off the floor) say: 'that wasn't very nice' and usually leave it at that. and make sure that i give DD a cuddle. also i then dont move too far away for a few minutes and if it looks as though the other child is coming back for more i place myself between them and DD as a way to allow her to continue her play and dissuade the other from choosing to do something not so nice (usually the short attention span of toddlers is a winner in this situation!).

I would think that the parent was really embarrassed and maybe has been having a hard time with the child, so chiding her may not be the most effective approach. this is of course to be put in context of whether the child is a repeat offender at the local park and it appears that the parents are just turning a blind eye IYKWIM. but for a once off at a supermarket i would let it pass (that said, i can throw a pretty disapproving glance when i want too, but again this is just more for my vindication that my girl was hurt than anything else).

HTH and hope your bubs is ok and not too shaken up!