A one-year-old boy died from neck injuries after being attacked by the family's bulldog, an inquest was told.
American Bulldogs have extremely powerful jaws
A verdict of accidental death was recorded on Liam Eames, who died in hospital after the attack in July.
The Leeds coroner was told by a vet the American Bulldog bitch may have been having a phantom pregnancy at the time.
She clamped her jaws around Liam and his mother could only pull him away after the family's other dog became involved, the inquest heard.
The child's father Christopher, who was at work when the incident happened, said he had brought the dogs inside their home in Woodnook Road, Leeds, because it was an intensely hot day.
He said his wife was sitting with Liam about 7ft away from the two dogs, which were both sprawled on the floor.
Mr Eames said the four-year-old bulldog, called Missy, then suddenly grabbed Liam as the baby began crawling towards her.
Missy had been in the household less than a year and had a "nervous" temperament, although Mr Eames said she had never shown signs of aggression towards Liam and his other son, Ben, aged five.
Trevor Turner - chief veterinary officer of Crufts and a vet with 40 years' experience - told the inquest it was probable Missy was suffering from a phantom pregnancy at the time of the attack and wrongly believed she had puppies.
He said: "The approach of Liam crawling towards her would be perceived as a threat and there would be a natural reaction.
"The dog behaved in the only way it could and guarded its personal space."
Mr Turner stressed Missy was an American Bulldog, not an American Pit Bull, and therefore not subject to the controls outlined in the Dangerous Dogs Act.
He said Missy had extremely powerful jaws with a bite pressure eight to 10 times that of a human.
Mr Turner said he would not advise any family to take in a large rescue dog without fully checking its history, and also giving it at least a year to settle in before introducing another dog.
West Yorkshire Coroner David Hinchliff told the court: "This is the time of the year people will acquire pets.
"I think the advice is that, though it's laudable to get rescue animals, it may be the younger the better so the child and the dog grow up together."
Mr Hinchliff said parents should also get as much information as possible about rescue dogs' backgrounds before buying them.