Previous studies have reported conflicting findings on children’s interpretation of additive particles. One of the previous studies has reported that Mandarin-speaking children up to 7 have difficulty deriving the presupposition triggered by the additive particle ye ‘also’. By contrast, another body of research has found that 3-to-4-year-olds can correctly interpret additive particles across languages. Such conflicting findings might have resulted from the different research techniques. Moreover, no study has been conducted to probe whether children are able to identify subject- versus object-associated focus in sentences with an additive particle. Against this backdrop, the current study attempts to systematically re-evaluate how Mandarin-speaking children interpret sentences with ye ‘also’, using an adapted research method. Two experiments were conducted with 3-to-4-year-olds and a group of adult controls. Experiment 1 probed whether children were able to identify object-associated focus in sentences with ye. Experiment 2 evaluated whether another group of children were able to identify subject-associated focus in sentences with ye. It was found that 3-year-olds already performed quite well and 4-year-olds nearly had adult-like performance in both experiments. The findings indicate that Mandarin-speaking preschoolers are able to identify subject- versus object-associated focus in sentences with ye, and such a linguistic ability develops in an incremental fashion. We discuss the methodological and theoretical implications of the findings.