Two young boys have drowned in separate incidents within 15 minutes of each other in Sydney's west.

An 11-month-old boy was found unconscious with his head in a bucket of water at a home in Fairfield East on Thursday afternoon, while just minutes later an 18-month-old boy was found floating in a backyard pool at a home in Greystanes.

Both boys were rushed to the Children's Hospital, Westmead, but died soon after.

In the first incident at 5.15pm, emergency services were called to a home on The Horsley Drive in Fairfield East where a boy was found unconscious with his head in a mop bucket containing about 10 centimetres of water.

The boy had been at home with his parents and six siblings when he wandered into the bathroom.