Hai mama, swelling dekat leher area tu memang boleh jadi few things, could be the glands (lymph nodes) yang bengkak sebab infection or something, but honestly with a 3-year-old I'd really suggest you pop by the clinic or see your paediatrician to check what's causing it, better safe than sorry! A few of us mums have had this happen with our kids during flu or viral season and it usually subsides once the infection clears, but the doc needs to rule out anything else first and make sure la.