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
Showers across Britain will make way for sunshine tomorrow before a milder end to the weekend, though heavy rain will return in the north.
George Clooney appeared in a special Downton Abbey as a host of stars came together to raise money for the ITV charity campaign Text Santa.
Events company Secret Cinema is planning to screen a film in protest at what they have called the 'censorship' of The Interview.