First of all, if rats aren't near to human food sources (or where, for example, they could chew the insulation on electrical cables) they're a perfectly harmless part of wildlife and I'd simply leave them be. (They won't harm your grandchildren!).
However, if you really feel the need to remove them, simply buy some humane traps, bait them and then deliver your new furry little friends into the countryside well away from any housing:
http://www.amazon.co.uk/The-Big-Cheese-Cage-Trap/dp/B000QVSCH6