Final answer:
For a routine capillary puncture, the ring finger is usually used in both adults and children because it is less prone to bruising, less sensitive, and has a thicker layer of skin, which may reduce pain.
Step-by-step explanation:
In adults and children, the finger usually used for a routine capillary puncture site is the ring finger (c. Ring finger). While the fourth finger, or ring finger, is typically the preferred site, the second choice is often the middle finger. These sites are chosen because they are less prone to bruising and are usually less used than the index finger and thus have a thicker layer of skin, which can make the puncture less painful. The thumb is not usually used because it has a pulse and can be more sensitive due to a thicker pad of skin.