Are there any rat owners left on Urban? My children have been watching youtube videos about training them to do tricks and are now desperate for some fancy rat pets. We'd need at least 3 - how big a cage should I be looking at?
For 3, one of the sides ( either vertical or horizontal ) should be about a metre long. Obviously if it's vertical then ladders, shelves etc are needed. Rats like to have a dark covered sleeping/hiding space, eating space and toilet space. Mine really like rat hammocks too.
Male rats are usually loyal lap rats and easier to tame and teach. You can't mix up male and female unless you want an ever expanding rat population. You could keep different sexes in seperate cages but they get lonely.
I've found that looking on Facebook or the tip shop for cages is the best bargain, currently we've got a 3 foot by 2 foot bird cage, the vertical type. And it's on a stand which both let's the cool air circulate better, and keeps it off a cold floor. There's 3 males in there and they have a top sleeping floor, a middle eating floor and a bottom toilet floor + their individual hammocks inbetween. This keeps it really easy to clean. But I get that not everyone has the space.
There are a whole lot of different models of rat

and theres a whole thing about if a rat has other rat mates they don't connect to their human and learn tricks so well. Don't become as domesticated .. but with three little humans I dont think that'd be an issue. It's a great project for kids

my kids always had a rat about their person somewhere, in a pocket, on their shoulder...
I've always found it best to get a couple of males, the babies are called kittens, from the same litter.