Is it okay to give a 1.5 year old triaminic? what is good for a persistent cough likely from allergies?

It depends: Children's Triaminic products can be given to a child of 18 months but only those with acetaminophen/dextromethorphan. Children's Triaminic products with pseudoephedrine (decongestant) or chlorpheniramine(antihistamine) should not be given to children under six years. If allergies are thought to be present than you need an antihistamine like cetirizine for children. Check with your pediatrician.