Police were called to an address on Frank Street, in the Little Horton area of Bradford, at 7.26pm yesterday and had to shoot the animal so paramedics could treat the boy.
A West Yorkshire Police spokesman said:
The child was then taken to Leeds General Infirmary where his condition this morning is described as stable, with injuries which are not believed to be life-threatening.
Inquiries are now ongoing as to the breed of the dog and to establish whether any criminal offence has been committed.
More top news
A backbench revolt over proposals to ease purdah restrictions on the EU referendum has led to a government climb down.
It's been a colder start to the day, especially in rural areas of Britain.
A viral video in which a French woman claimed she was trying to find the father of her baby has been confirmed as a hoax.