I spend a lot of time in the OTC aisle, and believe it or not , I get a lot of patients coming to me from their pediatrician with information about what active ingredients to take. In that case I usually explain what the product is and how it works, give safety tips, etc. If there is no ped recommendation, I restrict recommendations for children under 4 to a very small list of products, ibuprofen and apap usually, and give nonpharmacologic recommendations. There is occasionally a rare situation where I will recommend DM to the parent of a child in the 3-4 ish range, if they are INSISTENT, and will not settle for anything less, however I always follow it up with some disclaimers, and a hefty dose of education.
I would under no circumstances recommend a "combo" product, pseudoephedrine, or antihistamines for use in children under 4, except with specific written pediatrician instructions, as clearly their risks outweigh their benefits.
Most peds rec situations I run across are for apap/ibuprofen, (also some dextromethorphan) specific dosing regimens. I usually just help the parent figure out how to make up the dose.
Imho it's a clinical judgement call on each and every one of these. I don't have much experience to make clinical judgements at this point, so I trust the FDA, and clearly "risks outweigh benefits" on cough and cold products in children < 4, for the general population, so that's the rule i go by 99% of the time. I dont think pharmacists should be black and white in their thinking, but, they should listen to common sense at the same time.