"little child," 1725, Scottish, of uncertain origin, perhaps a shortened form of totter, or related to Old Norse tottr, nickname of a dwarf (compare Swedish tutte "little child," Danish tommel-tot "little child," in which the first element means "thumb"). Tot-lot "play ground for young children" is recorded from 1944.
"to reckon up," 1760, from tot (n.) "total of an addition," first recorded 1680s, short for total (n.). Hence, "to mark (an account or a name) with the word 'tot.'"
