The correct use of an affix, such as the English plural suffix, may reflect mastery of a morphological process but it may also depend on children's syntactic, semantic and phonological abilities. The present paper reports a set of experiments in support of this latter view, specifically focusing on the importance of the phonological make-up of plural forms for both production and comprehension. In Experiments 1 and 2 plural productions were elicited from eighty two-year-old children for nouns with codas with varying phonological properties. The results provide evidence that production of the plural morpheme is partly governed by the complexity of the coda and its sonority. Experiments 3 and 4 show that these constraints on codas also hold for comprehension as well, suggesting this effect is not simply articulatory, but also impacts the morphophonology of the plural.