Pretty pissed my 4 yo has a bruise on her arm like someone grabbed her or punched her. She can't…

Pretty pissed my 4 yo has a bruise on her arm like someone grabbed her or punched her. She can't remember who did it and at first she said the lady grabbed her then she changed the story to she did this to me and punched me. Thinking it was one of the older kids at daycare but regardless I'm pissed! No one should have grabbed or punched my kid hard enough to leave a bruise.