Then one said unto him, Behold, thy mother and thy brethren stand without, desiring to speak with thee. The verse is omitted by the Sinaitic manuscript (original hand), the Vatican, and a few others; also by the Old Syriac and some manuscripts of the Old Latin Version.
It is clearly an insertion to bridge over the "seeking" of Matthew 12:46 and "him that told him" of Matthew 12:48.