This article presents the results of research on the construction of mathematical study objects through the conceptualization of natural and social-crocodile objects in elementary mathematics learning in Makalehi Island and Marore Island, which are included in the border regions of the Republic of Indonesia. Mathematical conceptualization begins with the procedure of identifying, inventorying, and classifying natural objects, socio-cultural and formulating their interactions in the form of children's games and daily activities. The following process is the mathematical conceptualization of these objects through symbolization, quantization, concept or network of mathematical concepts and procedures, as well as synchronizing with mathematics learning materials in class. The results of the study identified several elements of natural and socio-cultural objects, which are the background of children's games and daily activities, which support elementary mathematics learning. The "bridge" of elementary school mathematics construction can use an inventory of some children's games and activities. A theoretical formulation as mathematical construction can be a hypothesis to be classified as good in terms of the meaning of symbols, quantization, the formation of concepts, or networks of elementary mathematics concepts. Theoretically, mathematical conceptualization like this has the potential to enable students to learn mathematics with ideal activities.