Infants and toddlers experience the world in interaction with others. Likewise, social interactions are important in learning about math--concepts of number ("one," "two," "three"), space ("on top," "upside-down," "round"), and magnitude ("more," "big," "tall"). As young children interact with caregivers during play, household routines, and other everyday activities, they receive critical input that reveals the math concepts present in daily life (e.g., Levine et al., 2010; Mendelsohn et al., 2022). Caregivers' math-related speech, in particular, is linked to children's own development of math language, which begins to emerge in the second year of life (e.g., Pruden et al., 2011). Despite growing recognition of the importance of early math interactions, research gaps persist on the experiences of infants/toddlers from diverse linguistic-cultural backgrounds as they engage with their mothers and fathers in the ecologically valid home setting. The three papers of this dissertation address these gaps. Paper 1 is a conceptual paper that synthesizes existing research, identifies gaps in the literature, and advances a linguistic and sociocultural approach to understanding early math interactions and language. Paper 2 empirically examines naturalistic infant-mother interactions at home to document the referents and social cues of English-speaking, U.S. mothers' everyday math language. Findings reveal that reliable and highly specific contextual cues are available to infants as they hear math language, which may facilitate learning such abstract words. Finally, Paper 3 is an exploratory, descriptive study that targets understudied samples and topics: I extend inquiry to fathers and mothers (rather than only mothers) and interactions of Latine, mostly Spanish-speaking families (rather than traditionally studied white, English-speaking families), and I zero in on spatial talk (rather than broader math talk including numbers) to toddlers during a parent-selected activity at home. Findings reveal the unique ways that Spanish-speaking parents use spatial terms (in verbs more than prepositions, etc.) and shows that their selected activities vary on spatial characteristics (e.g., blocks versus dolls), shaping the spatial language they use with toddlers. Together, these papers extend the study of early math interactions to infancy and toddlerhood, with an emphasis on sociocultural and linguistic contexts that are central to children's early experiences. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]