My 3 yr old son has a lump in his groin area. We just noticed it while changing him. He flinched when we touched it. What could it be.

Tender Mass. Hi, one of the barriers with children is they cannot always tell you what they are feeling, or what happened. A seemingly tender lump in the groin could be a lymph node, a hernia, an undescended teste, or abscess, I suggest a call to his pediatrician or visit to the er or urgent care for eval by trained professional. Good luck.
A couple of things. It could be an inguinal hernia or it could be an enlarged lymph node (gland). Your son should be examined by his pediatrician to determine exactly what it is and to prescribe the proper treatment.