How would you handle this situation ?

A coffee shop near me has a playground inside where kids can play and you watch them behind a glass . Usually they have somebody else inside who watches the kids but last day they didnt . I was watching my son play with the kids and they were all throwing little plastic balls to each other . They were all laughing and running and I was keeping an eye because I felt something would go wrong . . Another boy hitted my son in the face with a plastic ball and he did the same and the other boy started crying . I knew he would do that so I tried to get inside the playground before he hitted him but I was too late . When the other mom heard her boy was crying she came running yelling at my child because I was there talking to him that it was wrong that he did that .

I told her that she cant come here screaming at my child because in fact they were playing and got my son in my arms because he wasn’t understanding anything and went and sat on the table . She started yelling in front of everyone that i was a terrible mother , that i have teached my son that he should hit kids , that i should be embarrassed of myself because I am pregnant and rude . I said that you should be embarrassed for yelling so loud and my son doesnt hit other kids . He did that because he got hurt first and I went to stop that . She started yelling moreee and calling me a liar and asking her son if he did hurt my son first. She said apologize now and dont get your son out of there hugging him . I dont yell at my son and you dont know how we handle things . I was like would it make u happy if i got out of there yelling at him too? I was telling him to say he is sorry and asking why he did that and he was crying and telling me he hit him first and was apologizing to the other kid . I got out of there crying and feeling terribly about myself . I would apologize too but I didnt like her behavior. In the end they are little kids and they are going to get hurt playing but she couldnt ask for me to yell at my son .