Ethical and effective interviewing of young children in relation to their learning is a challenging and complex process. This paper describes the use of an experience-based flexible and focused interview methodology in a study based on young children's views and understandings of number. It shows how the approach used builds on previous work in relation to interviewing children for pedagogical purposes. The fourteen children interviewed as part of the study were just beginning school and they ranged in age from 4 years 1 month to 5 years 1 month. The nature of the interviews carried out with the children is discussed and characterised. This characterisation is in terms of the approach to the questioning; the focus on the exploration and development of the child's thinking; and the intensity of the experience for both child and adult. The flexible approach to interviewing taken in this study was seen to be very successful in eliciting children's views and understandings of number in a sensitive and ethical way. It is argued that such an approach can help to address some of the perceived difficulties with the use of an interview methodology with young children in educational contexts. It also illustrates how, in such conditions, children's agency is discernible; their awareness of metacognitive issues is expressed; and their numerical thinking is developed. The findings indicate that child interviews can be a powerful and effective method of researching and assessing children's learning. (Contains 4 tables.)