3 year old son for 24hours has a small red area on foreskin, with something that seems a piece of hair underneath the skin. doctor to remove it? me?

Do not remove it: first there isn't typically any hair in that area, so if gentle cleansing with baby wash doesn't clean it off, make appointment with pediatrician:)

Here are some ...: You may pull it out or remove it by gently retracting foreskin if feasible. Meanwhile, upkeep topical hygiene of the foreskin / glans penis by keeping the area as clean, dry, & ventilated as possible. But, if in doubt, seek professional attention timely. Best wish ...