I wouldn't leave ANY dog alone with a child. Dogs, unfortunately, are animals, and we seem to forget that. They can even do unintentional harm.
My dog is a yellow lab/whippet mix. He's the sweetest dog you could ever hope for. But he's really hyper and playful, and he thinks everyone wants to be his friend. He could hurt a small child unintentionally trying to play with it. (At 50 pounds, he doesn't realize his own strength, either).
Labs are excellent dogs. Our kids grew up with a black lab and now they each have a black of their own and they have kids. Never had the slightest problem with any of them. My son's is 90 lbs but very gentle.