Re the advice on getting a cat, I have it on good authority (the pest control man who was dispatched by Environmental Health to get rid of our rats) that dogs - particularly a terrier (jack russel terrier or border terrier in particular) are far more effective at catching rats than cats. Apparently cats are only good for the baby rats.
Other things to bear in mind - do you leave rubbish or food lying around outside? We don't have wheely bins provided by our council and used to keep full big bags in our garage until it was time for refuse collection. But the rats could smell it and chewed bits of the garage door away to get at the rubbish. The rubbish bags are now stowed in a galvanised steel container.
Also, after feeding the children outside on the patio I sweep up every remnant of food and hose it all down for good measure.