Hey dude, I worked at Toys R us during my student time at college and was there for two years. Theres so many different roles in the store, you have:
Front of Store which focuses on returns and complaints (stay clear). Then you have tills which is self explanitory (avoid, their outdated and always mess up)
You then have babies section which usually the female employees work on.
Theres the bike Isle (quite fun with the right people plus they'll teach you about bikes, very basic stuff though)
Then theres pickup, this is the area is your responsibility to collect larger items that cant be collected on the shop floor. People bring specific tickets for bikes and climbing frames etc and you have to run around half the store carrying heavy items all day. Id avoid this area as its knackering plus a lot of people got back problems from working on that section.
Then there's the best role, MULTIMEDIA. I cannot stress enough how much easier and more fun this section is compared to every other section. You work with all the electricals, games consoles, Tv's, PC's etc. You get to show everyone how stuff works and theres no heavy lifiting. Its the most simple job in the whole store and the most fun so WORK ON MULTIMEDIA. Express your interest in that area and they will make note of it. Even lie saying you build computers as its almost a guarenteed way of getting on it.
One last thing if the interviews are the same still as a few years ago be prepared to be there for around 2 1/2 - 3 hours. Its ridiculous but thats what they do. Make your voice known, speak up a lot and be prepared to pretend to sell an item to a customer through role play. The best advice I can give you though is dress in a suit, or shirt and tie, smart shoes. Its noticed and will impress, its one thing they have to check. Theres not much else to say, but if you want to talk my emails in my trust just drop me a line and ill help best I can. Good Luck!
edit: oh and the pay was around £5.40 when I was there, depends on your age though