Albert Barnes Commentary Acts 7:21

"and when he was cast out, Pharaoh`s daughter took him up, and nourished him for her own son." — Acts 7:21 (ASV)

Was cast out. When he was exposed on the banks of the Nile (Exodus 2:3).

And nourished him. Adopted him, and treated him as her son (Exodus 2:10). It is implied in this that he was educated by her. An adopted son in the family of Pharaoh would be favored with all the advantages which the land could furnish for an education.