littermate; litter (of animals)
Refers to animals born from the same mother at the same time. Can denote an individual littermate or the group as a litter.
These puppies are littermates.
I chose the most active kitten among the littermates.
Standard kanji spelling for littermate or litter.
Alternate kanji using 仔 (young animal); less common but seen in some contexts.
Compound of 同腹 (same belly) + 子 (child). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning.