The focus of this paper is to describe and discuss what resources toddlers' use to develop basic mathematical competence in a preschool setting. This development is described from the point of departure of the theory of variation and a Gibsonian view on perception, in terms of differences and similarities in a temporal sequence of situations where toddlers work with concrete materials such as building blocks of different kinds. The data consists of video documentations of children's everyday activities. We argue that we can see that the children have different ways of handling the tasks and situations at hand. The children can often discern where an object should be placed in relation to other objects according to relative size, orientation and rotation. When the task is changed, to a large extent the children has to "start from the beginning" often and has difficulties in generalising previous experiences, and previously used resources when working with other tasks.