Your language may have a particular way of introducing the person who receives a letter. Also, immediately after introducing the author, you may need to tell to whom the letter is written, as in the UDB.
"dear child" or "child whom I love. Here "child" is a term of great love and approval. It is also likely that Timothy was converted to Christ by Paul, and so this is why Paul considered him like his own child. Alternate translation: "who is like my beloved child" (See: [[rc://en/ta/man/translate/figs-metaphor]])