my son who is 3 recently had a trip to the drs for an ear infection and he started nursery in January, same as your little one with the constant colds etc he was at childminders before Jan so I guessed with nursery having more children there more bugs etc, his lymph nodes have always been more prominent in his right side, I ofcourse googled this and answer is usually cancer/death
I asked the dr and she said lymph nodes can actually stay prominent even once the cold/virus is gone, they can stay up even through till adulthood, if your little one isn’t showing any serious symptoms and it’s just the lymph nodes I wouldn’t worry, if in doubt get it checked out x