Infants’ social-cognitive skills first develop within the parent–infant relationship, but large differences between parents exist in the way they approach and interact with their infant. These may have important consequences for infants’ social-cognitive development. The current study investigated effects of maternal sensitive and intrusive behavior on 6- to 7-month-old infants’ ERP responses to a socio-emotional cue that infants are often confronted with from an early age: emotional prosody in infant-directed speech. Infants may differ in their sensitivity to environmental (including parenting) influences on development, and the current study also explored whether infants’ resting frontal asymmetry conveys differential susceptibility to effects of maternal sensitivity and intrusiveness. Results revealed that maternal intrusiveness was related to the difference in infants’ ERP responses to happy and angry utterances. Specifically, P2 amplitudes in response to angry sounds were less positive than those in response to happy sounds for infants with less intrusive mothers. Whether this difference reflects an enhanced sensitivity to emotional prosody or a (processing) preference remains to be investigated. No evidence for differential susceptibility was found, as infant frontal asymmetry did not moderate effects of sensitivity or intrusiveness.