WYM is frequently employed in cases when children need somebody to interpret or reword their message. As an illustration, when a friend makes a confusing or surprising remark, a child can respond, WYM? as a way of asking to get clarification. It is mostly used in quick conversations when it will be too long to type the entire phrase. The word in itself is not harmful but children can say it during a dialogue and may be sarcasm, argumentative or ambiguous so one should consider the context when decoding the use.
Know more: wym meaning