What can happen if a 5-year-old child sucked one adult pill of thyme and coltsfoot?

A single consumption of one lozenge intended for adults should usually not cause serious effects in the child, although irritation of the mucous membranes, mild allergic reactions, stomach discomfort or diarrhea may occur. It usually does not cause serious effects.

If you experience shortness of breath, severe cough, swelling or other alarming symptoms, consult a doctor or go to hospital immediately. In the future, you should avoid giving children herbs in adult doses without consulting a specialist.

If you need more personalized advice, you can use the teleconsultation here:

https://www.gdziepolek.pl/telekonsultacja/z-pediatra

I attach additional information that may be helpful:

https://www.gdziepolek.pl/artykuly/jak-bezstresowo-podac-lek-dziecku