Complex sentence: The first Danish children's book, "The Child's Mirror" by Niels Bredal in 1568, was an adaptation of a book of courtesy for children by the Dutch priest Erasmus.
Split into simpler sentences: The first Danish children's book, "The Child's Mirror" by Niels Bredal in 1568. This was an adaptation of a book of courtesy for children by the Dutch priest Erasmus.