body marks on a child I'm watching

im babysitting a friends brothers child and she is three. today was her first day and she had bruises and marks on her face, back, and butt as well as her arms. there were bruises and I'm not sure what the other ones could be. my guess is scrapes? how do I know the difference between normal marks and abuse? don't want to assume anything but I dont want to turn a blind eye or be blamed for this. not only that but i have a cps to lady coming to my house (ill be watching her child) and she'll see the little girl im watching when she comes by for a play date the day before she starts. i just want advice on what to do.