My own daughter mostly refused to wear socks - unless she had shoes on - until she was about five years old. Even now, she only wears them in the coldest months and rips them off her feet at the drop of a hat.
The three-year-old I now watch is pretty much the same way. With my own daughter, we had carpets and since the weather is pretty warm about ten months out of the year, I didn't worry about it too much and just kept her in sandals for outside.
However, with the young man I am caring for, his feet are always cold - even the rest of him seems fairly warm. I worry that his little feet are getting too cold. Should I be concerned, or just let him be?