<p>An open, non-comparative pilot study assessed the efficacy of a combined formulation containing melatonin and memantine (Miladean) as adjuvant therapy in 20 children and adolescents (8–15 years) with cognitive and behavioral disorders associated with hyperkinetic behavior disorder (F90.1, <i>n</i> = 7), schizotypal personality disorder (F21, <i>n</i> = 10), and schizophrenia (F20, <i>n</i> = 3). All patients received stable background therapy, to which Miladean was added for eight weeks (two tablets sublingually before bedtime). Cognitive tests (Raven’s Matrixes, Stroop test, computerized Go/No-Go test), sleep quality questionnaires (modified Spiegel scale), and the symptoms of attention deficit hyperactivity disorder scale (SNAP-IV) were used to evaluate progress. The medication demonstrated a good safety and tolerability profile. There were significant reductions in symptoms of inattention and hyperactivity–impulsivity on the SNAP-IV scale (<i>p</i> &lt; 0.001), along with improvement in sleep quality (<i>p</i> = 0.002) and an increase in reaction speed in the Go/No-Go test (<i>p</i> = 0.001–0.033). A tendency towards improvement in performance on the Raven’s matrixes intelligence test (<i>p</i> = 0.067–0.077) was noted. The preliminary data obtained here indicate the potential effectiveness of Miladean in correcting cognitive and behavioral disorders in children in the contexts of a variety of disorders and provide grounds for further double-blind placebo-controlled studies.</p>