They're essentially the same as 9 mm, which is the go-to defensive handgun of choice for most of the world's population. It's not a small caliber by any stretch, and the size of the gun doesn't matter.

That said, a panicked mother protecting her child will almost always react poorly to the kickback, handle the thing like shit, and be unaccustomed to low-light situations. She probably aimed at his head and got a predictably poor grouping. It's not surprising nothing major was hit, really.

Also, bear in mind that they probably were fatal shots. Pistols rarely ever stop someone dead in their tracks, unless one hits a major organ or is using a large enough caliber to deal severe nerve damage. The movie scenes involving the hero shrugging off bullets actually are closer to the truth than you might think. Instead, the victim dies of blood loss minutes later, and can remain conscious throughout. My best was the fucker was bleeding out when they got him.