Hello. My Three And Half Years Old Son Has Lymph

Hello. My three and half years old son has lymph nodes on both sides of his arms. They are 2-3 inch above the elbows at the inner side of his arms. I never noticed them before. They are soft and moveable. Around 1-2 cm in size. Apparently my son is healthy. No apparent infection. What is it? Do I need to concern? Thanks