Sarah (Decker) Purcell given slave by father

During research into the Battle of Tippecanoe, I found that Sarah Decker(b.1778)was given a slave (Ann) by her father John Decker (b.1750)in his will dated August 4th 1790. A notation concerning the will indicates that the slave had already been given to Sarah sometime prior to the filing of the will in Knox County, IN.

So, at the time the will was filed, Sarah would have been about twelve years of age and had already been given the slave (Ann) prior to the filing.

Question: Would it be customary for a slave to be given to and owned by a minor child - particularly one at or under the age of twelve?