Hey guys so I need some help making a decision to reach out to authorities or am I just overreacting???

I work with a single mom who lives at home with her parents and siblings and one night after a fight she moved herself and her son out and bounced from coworker to coworker. She began to ask me for money and I felt like it was the right thing to do so I let her have a hundred dollars. However, she came to work a few days later with her nails done. She asked me to watch her son one day and I agreed. He bangs his head around for attention or if he is upset. He has bruises on his head and a helmet he can wear to make it hurt him less. He is almost two years old and says nothing. He was so happy to be with me and when I had to give him back to his mom he began to scream and hit her. I guess this is common for him. The other day I bought him some lunch because she complained he was hungry and had no money. He clings to me for dear life when we are together. I’m not sure what more I can do for her or her child. I’m just worried for him because of his head banging, the fact that she can’t afford gas or food for him and that he is often just left in the crib. I’m not trying to mom shame or anything I just need some advice. She has also moved back in with her family so she is not homeless.