Is it normal for my almost 6-month-old not to roll over yet?

My daughter is almost 6 months old, weighs 17 pounds and is about 26 inches long. She's in the 95th percentile for both height and weight. She is healthy and progressing well, except that she won't roll over. Is this normal? I'm worried that she's too fat and can't roll over properly.

Your daughter is a big girl. Heavy children do have a harder time moving around, so some of the motor developments do appear later. The normal range for rolling from front to back is 4 to 10 months. Since you can't predict when your daughter will master this milestone for the first time, never leave her unattended on a bed or changing table. I'd ask your GP to check her development at your forthcoming six-month visit. Get him to check your daughter's motor tone or muscle tension to make sure it is normal. Go over her diet to be sure it's balanced. My guess would be that all is well, but that is why we have these regular visits during early childhood - to check on all of the child's progress.