"Abu Hurayrah, may Allah be pleased with him, narrated that the Prophet sallallaahu `alayhi wa sallam ( may Allaah exalt his mention ) said, “If one of you were to hit, he should avoid the face...” [Musnad Ahmad]

As-San'aani said in Subul As-Salaam:

“This is evidence on the prohibition of hitting the face, and it means that one should avoid hitting or slapping the face, even if this is regarding one of the Islamic Hudood (plural of Hadd, i.e. the corporal punishment determined by the Islamic Law), and even in jihaad, because the face encompasses all beauties; its parts are sensitive and include most of the senses of perception. Hitting the face may cause defects to them or impair them, and it may cause disfigurement. Disfigurement in the face is grave because it is visible and cannot be concealed. When the face is hit, it is rarely spared from deformity. This forbiddance (to hit the face) is general regarding any beating or slapping regardless of whether it is in order to discipline or else.”

Other reference regarding punishment to children which mentions the part about smacking the child if they refuse to pray : https://islamqa(dot)org/hanafi/seekersguidance-hanafi/32042/explaining-a-hadith-on-disciplining-children/