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It's probably just a hydrocele -- a fluid-filled sac that surrounds the testicle. It's not a cause for alarm: In fact, 10 percent of baby boys are born with hydroceles and it usually goes away without treatment by age 1. Or your child may have a hernia, a protrusion of part of the intestine through a weak area in the wall of the abdomen and into the scrotum, which can occur during fetal development. (Girls can get a hernia in the groin area as well, though the problem is more common in boys.) A hernia feels soft, and you'll be able to push it back into the abdomen. Your child will need surgery, but there's no rush unless the area is extremely tender and red -- signs that the hernia is stuck. The lump could also be an enlarged lymph node, especially if it's located where the leg and torso meet. Lymph nodes are part of the immune system, so whenever your child has inflammation or an infection -- even from something seemingly minor like a cut or an insect bite -- they swell to protect the body. When the infection clears up, the lump will also disappear. In rare cases, if the lump is rock-hard and immovable, it may be a tumor, though don't start freaking out: Cancer in a baby's groin area is extremely uncommon. Leukemia also causes lymph nodes in the groin area to swell, but you'd also notice enlarged nodes in your child's neck and armpits, along with weight loss and paleness. Regardless of the cause, you should get any lump evaluated by your pediatrician. --Donna Christiano
Originally published in Parents magazine, November 2007. Updated 2009
The answers from our experts are for educational purposes only. Please always refer to your child's pediatrician and mental health expert for more in-depth advice.