The kits are born partially naked and blind. At birth, they weigh 3 grams. Long-tailed weasels grow fast. By the age of three weeks, the kits have lots of fur. They can crawl outside the nest and eat meat. At five weeks of age, the kit's eyes open, and the young become active. At this stage, the kits are weaned. The kits are fully grown by autumn. They leave the family at this time. The females are able to breed at 3–4 months of age. Males become sexually mature at 15–18 months.