Final answer:
The first action by the nurse when a soft, boggy uterus is palpated is to initiate fundal massage. Fundal massage helps to stimulate contractions and promote uterine involution after childbirth.
Step-by-step explanation:
The first action by the nurse when a soft, boggy uterus is palpated is to initiate fundal massage. Fundal massage helps to stimulate contractions and promote uterine involution after childbirth. It involves applying firm, gentle pressure to the top of the uterus to increase uterine tone and prevent postpartum hemorrhage. Assessing the maternal vital signs would also be important to monitor the mother's condition, but initiating fundal massage is the most immediate and specific action to address the soft, boggy uterus.