Digimon Frontier: Island of Lost Digimon

デジモンフロンティア 古代デジモン（オニスモン）復活！！

The five digi-destined children stumble upon an ancient island inhabited by two different types of digimon; The Beast types, and the Human types. When they see two young digimon-a beast and humanoid-have become friends, they decide something must be done about the feud. (Source: ANN)