There is no reason to panic at all. If the lump is a small one, rubbery in nature,movable and is not painful to touch and slips under your finger ,you are probably dealing with a lymph
node that is enlarged.It is usually caused by local infection near the genital area or groin.
Have a nice look at those areas. The lymph nodes have enlarged to combat that infection. Treating the problem will decrease the size of the swelling. But do consult your local paediatrician for an examination.
Don't worry ,everything will be fine.Have anice day