From time to time the debate over whether early-onset epileptic seizures are harmless or have harmful effects on the developing brain reappears. We evaluated the results of clinical studies reporting the long-term cognitive development of children who suffer from early-onset epilepsies, that is to say, in children with brain immaturity: neonatal epilepsies, West's syndrome, Dravet's syndrome, benign myoclonic epilepsy in infancy, myoclonic-astatic epilepsy and Lennox-Gastaut syndrome; we also report on the harmful influence of certain antiepileptic drugs, such as phenobarbital and valproate, on the immature brain. The negative repercussion of early-onset epilepsies on the immature brain is unquestionable, with sometimes very intense impairment of cognitive development. As a result, we make the following recommendations: early electro-clinical diagnosis, immediate treatment, timely change of medication if the seizures persist, avoid phenobarbital and valproate, and try other drugs or compounds that have proved to have neuroprotective effects in experimental studies.