My Brother's Drawing (Chilling Deduction)

I have a 5-year-old brother who tragically passed away in a car accident six months ago. My mom, overwhelmed by grief, started showing signs of mental distress. She would sit in the living room every day, holding the teddy bear my brother loved most, and talk to herself. Today, while organizing my brother's belongings, I found a sketchbook he drew in under his bed. The last page's doodle depicted our family: Dad, Mom, me, and my brother. Everyone was smiling happily, but strangely, my brother used a red crayon to draw a big red circle on Mom's belly.