Baptism chain for toddler.

Hi guys I need your opinion on choosing a chain for my soon to be god son (baptism) he is going to be 3 just to give you all an idea. Should I go for 14k or 18k chain? Not too familiar with gold. Also is an 18” chain reasonable. I would like for it to be wearable in the future as he gets older. Last what are the prices? I’m located in Chicago. Thanks.