In February 1406, Sir John Stanley was granted free warren of the Manors of Lathom and Knowsley in his wife's right. (The Manor of Knowsley is still held by his descendant, the Earl of Derby, while the Manor of Lathom remained in the Stanley family until 1717, when it was sold by the daughter of William Stanley, 9th Earl of Derby.) It was about this time that Sir John Stanley adopted the crest of an eagle and child which has been used by his descendants ever since.

Before this time it is likely that he used the family crest of the Stanleys of Stourton, i.e. a stag's head, which was the crest used by his elder brother, Sir William Stanley of Stourton and his descendants, the Stanleys of Hooton in Cheshire, who were the senior branch of the family until their male line died out in the late 19th century. This crest of a stag's head is still used by the other ancient branch of the family, the Stanleys of Dalegarth and Ponsonby Hall in Cumberland, who branched off from the Stanleys of Stourton about 1335· Many legends exist about the origin of the eagle and child crest of the Stanleys which was probably taken from the crest of the Lathoms. One account tells of a Sir Thomas Lathom who greatly desired a male heir, but his wife was advanced in years and their only child was a daughter. One day, he and his wife were walking in Tarlescough Woods, a wild section of his estate when they heard an infant crying. Servants were sent to investigate and they returned with a young male child which they had found lying in the grass below an eagle's eyre. In another version, it was discovered in an eagle's nest. The child was well dressed, and Sir Thomas and his wife decided to bring it up as their own son, naming him 'Oskatel'.

The tradition of a child being found unharmed in an eagle's nest is very old and exists in folklore in many parts of Europe, notably in Norway and France. King Pepin was said to have discovered a child in similar circumstances, and another tale exists that King Alfred the Great found a child after hearing it crying while he was out hunting. When his servants investigated, they discovered a male child in an eagle's eyre, dressed in purple with gold bracelets on its arms (the mark of Saxon nobility). The King named it 'Nestingium' and had it baptized and educated. It has been suggested that these old tales gave Sir Thomas Lathom the idea in the first place, when despairing of a son by his wife, he is said to have had an intrigue with a young gentlewoman whom he kept in a house nearby. She gave him a son, and his problem was to get it recognized and accepted by his wife in such a way that her mind would be free of jealousy. He thereupon arranged the whole thing, and the child was brought up as her adopted son and made heir to part of his estate. However, on his deathbed, Sir Thomas confessed that Oskatel was his bastard, and his daughter, being his only heir, inherited the whole estate. However, he made provision for his natural son by settling upon him and his heirs, the Manors of Islem and Urmston near Manchester, and Oskatel is said to have been the founder of the Lathoms of Earlham. There is a stained glass window in St Wilfred's Church at Northenden bearing the name of Oskatel de Lathom and his crest. The original Lathom crest was an eagle, head turned back as though looking for its prey. Sir Oskatel adopted a similar crest of an eagle looking away from a child as if it was defying all that might harm it. The only daughter was said to have been Isabel de Lathom who married Sir John Stanley. However, Isabel's father had three sons and had no need to resort to a device to adopt an illegitimate son in order to keep his estate together. If there is any truth in the story, then it is likely that the Sir Thomas Lathom concerned was Isabel's father's eldest son, also Sir Thomas Lathom who died in 1383, leaving an only daughter, Ellen, who died without issue in 1390. Her two uncles had predeceased her, thus making her aunt, Isabel, the heir. If Ellen's father had a natural son who was claiming part of the estate, it might explain the delay from 1390 to 1406, when Lathom and Knowsley were granted to Sir John Stanley in his wife's right. It was then said that Sir John adopted for his crest an eagle looking down on the child as if it was about to devour him, in order to emphasize the triumph of the legitimate heiress.

Several experts have pointed out that the very nature of hawks and eagles makes it unlikely that a child could be carried off by these rapacious birds and yet remain alive. Generally, they kill their prey as they strike. They only use an eyre when they have young and they then tear and rip their catch into small pieces with which to feed their offspring. Furthermore, it is considered unlikely that a child so richly dressed should be left unprotected at the mercy of wild animals and birds of prey as stated in the legends. However, experts can be wrong. In May 1959, the English Press reported that a three-year-old boy, Mariano Mesels, was out with his father in the mountains near Vicarza in Northern Italy, when he was snatched up by a large eagle and carried off to a mountain peak 4,300 feet high, where the child was later found between two big boulders after a search lasting thirty-six hours, unhurt, but suffering from the cold because his clothes were in shreds.