Periodontal diseases are among the most frequent diseases affecting children and adolescents. These include gingivitis, localized or generalized aggressive periodontitis (a.k.a., early onset periodontitis) and periodontal diseases associated with systemic disorders. The effects of periodontal diseases observed in adults have earlier inception in life period. Gingival diseases in a child may progress to jeopardize the periodontium in adulthood. Therefore, periodontal diseases must be prevented and diagnosed early in the life. This paper reviews the most common periodontal diseases affecting children: chronic gingivitis (or dental plaque-induced gingival diseases) and aggressive periodontitis. In addition, systemic diseases that affect the periodontium in young children and necrotizing periodontal diseases are addressed. The prevalence, diagnostic characteristics, microbiology, host- related factors, and therapeutic management of each of these disease entities are discussed.