All circulating immunoglobulin G (IgG) antibodies in human newborns are of maternal origin and transferred across the placenta to provide passive immunity until newborn IgG production takes over 15 weeks after birth. However, maternal IgG can also negatively interfere with newborn vaccine responses. The concentration of IgG increases sharply during the third trimester of gestation and children delivered extremely preterm are believed to largely lack this passive immunity^,,. Antibodies to individual viruses have been reported^{, , , , , , –}, but the global repertoire of maternal IgG, its variation in children, and the epitopes targeted are poorly understood. Here, we assess antibodies against 93,904 epitopes from 206 viruses in 32 preterm and 46 term mother–child dyads. We find that extremely preterm children receive comparable repertoires of IgG as term children, albeit at lower absolute concentrations and consequent shorter half-life. Neutralization of the clinically important respiratory syncytial virus (RS-virus) was also comparable until three months of age. These findings have implications for understanding infectious disease susceptibility, vaccine development, and vaccine scheduling in newborn children.