If your pediatrician says Children's Motrin is acceptable, I just checked and Costco has that available.

From what I've been told by a pharmacy manager and our doctors, cold and flu-related meds are in high demand this year because of RSV, the flu going around, and still COVID, so there are going to be shortages. We had a bad cold pass through our house, and after it was determined not to be COVID after multiple tests, we were told just to stay home and rest. For a week, I was burning through Mucinex and Advil until we felt well enough to get to Costco who had plenty.