“The knots are like small pendants at the bottom of the garment, created by tying part of the fabric around substances known for their protective qualities: resin, salt, iron sulfate, asphalt, henna, seeds, and other unidentified materials. The binding was done by winding a flax thread around the material several times,” says Dr. Orit Shamir, Israel Antiquities Authority textile specialist…
…it may be speculated that the knots were hung on it to protect the child from illness and harm. “You can really imagine a mother hiding salt for protection and tying up a piece of the flax garment while reciting prayers and hopes for her son or daughter,”

Sounds like a Tzitzit to me…