The number of children Poseidon fathered is debatable, but at least a hundred children are said to be his offspring. Poseidon was much like Zeus with his love of women and numerous offspring.
Poseidon had a number of children that are well known in Greek mythology and not all of them were human in form. His son Triton was a merman who could change shape at will. It is said that his union with Medusa on the floor of the Athena temple produced Pegasus, the winged horse, and Chrysaor, who appeared human. The child Poseidon had with Demeter was a stallion who could talk, due to their joining while they were both in the form of horses.