Immunizations early in life, when the host is most susceptible to infection, allow protective immunological memory to develop. Decreasing the dose of Cas-Br-E murine leukemia virus when priming neonatal mice results in adult-like, Type 1 protective responses, but the resulting memory cell populations are smaller than after adult priming. After secondary challenge, virus-specific CD8+ memory cell populations expand twice as much in neonate-primed mice as in adult-primed mice. We found that when equivalent numbers of virus-specific cells were transferred into virus-susceptible mice, protection from disease was similar whether donor, immune mice were primed as neonates or adults, and IL-4 did not alter in vivo virus-specific CD8+ memory cell effector function. Hence, neonate-primed CD8+ cells develop into memory cells that rival adult-primed cells in proliferation and effector function.