Previous research has demonstrated that being bilingual from birth is advantageous for the development of skills of social cognition, executive functioning, and metalinguistic awareness due to bilingual children's extensive experience of processing and manipulating two linguistic systems. The present study investigated whether these cognitive advantages are also evident in sequential bilinguals, i.e., children who began the acquisition of their second language later in childhood. Monolingual English-and English-speaking children acquiring Welsh as a second language matched in age (M age = 4.6), and English receptive vocabulary completed three tasks of attentional control, metalinguistic awareness, and metarepresentation. Sequential bilinguals outperformed monolinguals in the task of attentional control, while no differences were found in the metalinguistic awareness and metarepresentation tasks. These findings suggest that attentional control is the first cognitive component advantaged by early sequential bilingualism and further highlight the benefits of second language exposure in the context of early formal education.