Would you be inclined to buy makeup because a 10-year-old boy is showing you how to create a look on Instagram? If we’re talking about Jack Bennett of @makeuupbyjack, then the answer could well be a resounding yes. Since convincing his mother to start his account in May, young Mr. Bennett, who lives in Berkshire, England, has amassed 331,000 followers and attracted the attention of brands like MAC and NYX, which have offered products to create looks. Refinery29 has celebrated him as the next big thing in makeup. He is the latest evidence of a seismic power shift in the...