A son of peace (huios eirēnēs). A Hebraism, though some examples occur in the vernacular Koiné papyri. It means one inclined to peace, describing the head of the household.
Shall rest (epanapaēsetai). Second future passive of epanapauō, a late double compound (epi, ana) of the common verb pauō.
It shall turn to you again (eph' humās anakampsei). Common verb anakamptō, to bend back, return. The peace in that case will bend back with blessing upon the one who spoke it.