These are the Rebbe's letters to individuals about their own situations. Throughout, the Rebbe instructed people to consult an expert doctor and follow his guidance; anyone facing a medical question should do the same.
The Rebbe's guidance to parents whose child is unwell or struggling:
Follow the medical advice, and strengthen your own trust in Hashem. A parent's faith and bitachon matter greatly when a child's health is uncertain; be cautious about unproven procedures (IK 1636, 7682). Follow up with the doctors promptly and consult carefully before medical decisions for a child, such as removing tonsils, and keep careful medical oversight of medications like antibiotics (IK 1387, 4299, 7129, 7656). Even when the medical opinions are grim, don't give up hope; keep consulting the experts (IK 7604). When a child is hospitalized and resists treatment, rely on a trusted doctor to persuade him rather than confronting him directly (IK 10948).
Spiritual steps for the child's wellbeing: check the tefillin and mezuzos, observe taharas hamishpacha carefully, and wear a tallis katan and yarmulke (IK 1528, 4259). Keep Torah study central in the child's life, for his physical as well as spiritual wellbeing (IK 7018). Increase in Chassidus study as a segulah for children (IK 1387), and in involvement in Jewish education, which brings merit for one's own children's healing (IK 569).
Stuttering: combine practical help, medical advice and a supportive environment, with checking tefillin and strengthening Torah study (IK 1706, 8371, 9175).
Sleep and night waking: alongside checking tefillin and mezuzos, pay attention to the child's education; the Rebbe also confirmed stopping medication where it wasn't needed (IK 4259).
Child rearing: follow the balanced middle path of the Rambam, taking the medical advice into account (IK 7300).
Timing and health: a bris milah takes place when the baby is healthy, without unnecessary delay (IK 2003). Starting cheder slightly early is fine if a doctor approves (IK 1924). With a young child, avoid unnecessary travel and follow the doctor's advice (IK 10757, 10886).
Don't despair; serve Hashem with joy and trust, and this brings blessing to the whole family (IK 2529).