When capturing the adorable facial expressions of a baby in a drawing, it's essential to observe and study their unique features closely. Pay attention to the curvature of their cheeks, the size and shape of their eyes, and the subtle details of their tiny nose and mouth. Focus on capturing their innocence and curiosity through their expressions, whether it's a toothless grin, wide-eyed wonder, or a playful pout. Adding light and shadow to emphasize the contours of their face can help bring depth and realism to your drawing. Remember to keep your lines soft and gentle, reflecting the tender nature of a baby's features.