Abstract: In exemplary implementations of this invention, a warmer is configured to hold warm water and a container of chilled or frozen breast milk, and to heat the breast milk by heat transfer from the water to the breast milk. The warmer may comprise a vessel (for holding the warm water), flexible bristles and a lid/dome. The vessel is insulated by a vacuum layer. The water can be poured into a cavity in the vessel. The vessel is penetrated by a hole that opens into the cavity. In exemplary implementations, the flexible bristles protrude into the hole, and are configured (i) to be elastically deformed when a human user inserts or removes a breast milk container through the hole, and (ii) to inhibit bobbing of the container, due to buoyancy.