Which sign indicates a possible serious allergic reaction in children?

A severe swelling of the lips and tongue is indeed a significant indicator of a potential serious allergic reaction, commonly associated with anaphylaxis. This swelling, known as angioedema, can obstruct the airway and lead to breathing difficulties. It signals that the body is experiencing a robust immune response, which can be life-threatening if not addressed immediately.

Other options, while they may suggest some level of allergic reaction, do not carry the same urgency. For instance, a skin rash alone may not indicate severe systemic involvement, especially if there are no other accompanying symptoms. Similarly, shortness of breath without chest tightness or an itchy skin sensation in isolation suggests less severe reactions that might still require attention but typically do not pose an immediate life-threatening risk like severe swelling does.