Friend’s child is giving off major body odour

My friend has acknowledged in passing that her child (13f) is a stinky one. I’ve had her and her little sister over twice now (they love spending time with me). The child reeks, and the stink fills the room. The last visit, I gently invited her to change into a “fresh” pair of clothes—the smell continued. She showered before she arrived and the smell persisted. I casually spoke to her and her sibling about the importance of hygiene so as not to single her out. Not sure what to do because I don’t want them to come over again unless I can breathe! But also I am concerned about how this will affect the child socially.