Sometimes a fostered child Might tell you something and ask you not to tell anyone. This might be something they have done recently (for example if they have broken something in the house) or about something that has happened to them in the past.
Sometimes it easier to trust someone who is closer to you in age that to trust an adult. Someone who is being fostered by your family may tell you something they have not told anyone else. This can be very upsetting for you, particularly if they tell you something bad that someone might have done to them in the past.