Older child throwing sand at my 8mo daughter.

I was at the park with my daughter and husband today, she was sat in the sandbox with my husband playing with the sand. A little girl who looked 4 maybe 5, came over to the sandbox and started throwing sand on my little girls head. She was wearing a sun hat which at least stopped it falling into her eyes. We told the girl nicely to stop doing it because it could end up in her eyes and hurt her multiple times, but she kept throwing the sand. Her mum was stood with her back to the sandbox talking on the phone. I had to approach the mum and tell her that her little girl was throwing sand at my 8 month old, the mum yelled at me for interrupting her on the phone, screaming "can't you see I'm busy?" I walked away without replying and took my little girl to play elsewhere on the park. How would you handle this situation? I feel really upset by it. via /r/Parenting https://ift.tt/2skVVLL