Three-week old Reggie was rushed to hospital following the attack by the Patterdale terrier – but doctors were unable to save him.
His family have said they are "trying to cope" with the immense tragedy of losing little Reggie, who lived at Falkland Road with his parents Maria Blacklin and Ryan Young, a builder.
The parents are said to be “distraught” after the tragedy which happened at their home at 4.15am yesterday.
A family member who spoke to the Chronicle outside Ryan's family's home nearby said: "We are trying to cope with this the best we can."
Their family dog, called Tricky, is being kept in kennels and is expected to be destroyed.
Northumbria Police said a 30-year-old man had been arrested in connection with the incident.
“We are carrying out enquiries to establish the circumstances.”
The source said she had been at a family event following a bereavement, and had returned to find the distressing scene.
Neighbours yesterday spoke of their shock at the death of Reggie, who is believed to have four brothers and sisters.
One, who did not wish to be named, said: “I know terriers very well. I think the dog had become jealous of the baby and that is why this has happened.
“It was Ryan’s dog as far as I’m aware. He is a lovely lad, hard-working and an excellent father. He will be devastated.”
Criminal psychologist Paul Tweddle, 50, who lives opposite the family in Sunderland, Tyne and Wear, said: “They are a caring couple in their 30s and are a lovely family. This is a complete tragedy.
“I see the terrier from time to time. Sometimes I see it clambering at the fence and it gets out so I shout to Ryan and he comes and gets it.
“It is a tiny dog and I cannot say whether or not it is dangerous. Sometimes appearances can be deceptive.
“I am so shocked. It should be such a happy time with a new baby. I have children myself, so you can imagine how I am feeling.”
Another neighbour, Denise Haley, 59, is grandmother to a six-week-old baby called TJ.
She said: “Maria was in the house a few weeks ago with Redgie. She is a lovely girl and I simply do not know how she will cope with this tragedy.
“I am scared of any dog but that dog seemed okay. It is a tiny dog and brown in colour.
“I am in total shock – me and my daughter have been really upset about it. We grabbed TJ straight away and gave him a huge hug.”
Source: UK Mirror.