In 1994, 62 children claimed to have had an alien encounter. John E. Mack, a Harvard Professor, traveled to Ruwa, Zimbabwe to investigate. The video quality is not great but it's worth a look. Witness testimony - how could 62 children lie and stick to their story - the only other explanation could be a mass hallucination.
62 Children Encounter Aliens Part 1
62 Children Encounter Aliens Part 2