The following is from The Religion of Ancient Egypt by William Flinders Petrie, Edwards Professor of Egyptology, University College, London (1906):
Isis became attached at a very early time to the Osiris worship; and appears in later myths as the sister and wife of Osiris. ... The union of Horus with the myth, and the establishment of Isis as the mother goddess, was the main mod of her importance in late times. Isis as the nursing mother is seldom shown until the twenty-sixth dynasty; then the type continually became more popular, until it outgrew all other religions of the country. In Roman times the mother Isis not only received the devotion of all Egypt, but her worship spread rapidly abroad, like that of Mithra. It became the popular devotion of Italy; and, after a change of name due to the growth of Christianity, she has continued to receive the adoration of a large part of Europe down to the present day as the Madonna.
Horus became identified with the sun-god, and hence came the winged solar disk as the emblem of Horus of Edfu ... the infant Horus with his finger to his lips was the most popular form of all, sometimes alone, sometimes on his mother’s lap. ... From the twenty-sixth dynasty down to late Roman times the infant Horus, or the young boy, was the most prominent subject on the temples, and the commonest figure in the homes of the people ...
Isis and Horus, the Queen of Heaven and the Holy Child, became the popular deities of the later age of Egypt, and their figures far outnumber those of all other gods. Horus in every form of infancy was the loved bambino of the Egyptian women. Again Horus appears carried on the arm of his mother in a form which is indistinguishable from that adopted by Christianity soon after.
We see, then, throughout the Roman world the popular worship of the Queen of Heaven, Mater Dolorosa, Mother of God, patroness of sailors, and her infant son Horus the child, the benefactor of men, who took captive all the powers of evil. And this worship spread and increased in Egypt and elsewhere until the growing power of Christianity compelled a change. The old worship continued; for the Syrian maid became transformed into an entirely different figure, Queen of Heaven, Mother of God, patroness of sailors, occupying the position and attributes already belonging to the world-wide goddess; and the Divine Teacher, the Man of Sorrows, became transformed into the entirely different figure of the Potent Child. Isis and Horus still ruled the affections and worship of Europe with a change of names.