Avoid if poss. Diarrhea is a natural mechanism to clean the intestines from toxins or pathogens. Drs. Advice to avoid anti diarrheal medications if possible always. The main issue is to keep good hydration, drinking fluids and electrolytes (potassium & sodium) to replace the loss and to maintain good hydration. Ask ur pediatician.
Most likely no. Imodium (loperamide) is not to be used at all under 4 years of age. Over that, it may help a little, but for the most part, keeping a child well hydrated, and keep them eating with a well balanced, and, oddly, a slightly fatty diet, will help. Probiotics restore balance in the gut and can help reduce the duration of the diarrhea. Also avoiding dairy for a few days, since some kids become lactose intolerant.