This chapter is a first step towards the characterisation of the morphological structure of the French lexicon in early first language acquisition, i.e. before children coin novel word formations. Focusing on nouns and verbs, it analyses the variety of derivational means used by toddlers and caregivers in two corpora of French-speaking children (1;4/1;6-2;11). A comparison is done with a sample of adult-directed speech (ADS). Findings on derivation are compared with previous observations on compounds in the same data. The results display the development of tight-knit morphological relationships within the lexicon and a clear prevalence of suffixation over other derivational means and compounding. Along with errors in affixed words, these relationships provide cues of early detection of derivational morphology in child speech.