A 2-year-old male is brought to the emergency department by his mother. The patient awoke in the night screaming, and when the mother changed his diaper she found thick, bloody stool. The child was born at 35 weeks, via c-section, and required an overnight stay in the NICU for tachypnea. Developmentally, the child is at the 38th percentile for weight and has met all milestones. The child's pulse is 110/min, blood pressure is 90/60 mmHg, and respirations are 20/min. An abdominal ultrasound is obtained, and shown in Figure A. What is the next best step in management?