Rats are amazing for children! If you are near Brighton I'll happily bring my boys to meet you if you need convincing :) I am now going to apologise for the essay that follows! Sorry!
The cage would be too small, the width and length are great, but rats need height for climbing. Tunnels and toys designed for hamsters are too small for rats as well, our cage came with some tunnels and our boys grew out of them by 10 weeks. One of our girls could possibly use them, if not both, but they are very small for year old females and I still wouldn't risk it.
We bought this cage for our boys:
www.littlepetwarehouse.co.uk/little-friends-narrow-hamster-cage-p-16514.html
Which I think is okay, the doors aren't a great size and the shelves it comes with were getting a bit too bouncy by the time we bought a new one but it does well for the girls we have in it now. Our boys are in this:
www.littlepetwarehouse.co.uk/coco-hamster-cage-with-platforms-large-100x70x54cm-p-16580.html
The wooden shelves will need replacing and we don't use the ramps at all, but it's a nice sized cage.
Rats come in varieties rather than breeds, as long as you get them from a good breeder you'll have a good rat. If you aren't fusse don varieties then you have amuch wider range and also won't need to worry about waiting lists. Our boys are beautiful but because they aren't specifics we got them with two weeks notice, however when we buy another pair we'll be going for a pair of dumbos, for which our relatively local breeders need three+ months notice for.
Go for an NFRS breeder, they have certain standards that they need to maintain and the rats should be friendly as anything.
Boys are lazier, but they are happier being shoulder rats. Our girls are just as active as the boys are funnily enough, but when out and about they are happier in our jumpers, whereas the boys like freeranging a lot more. This could be because our girls are rescues and though we've had them for two months, they are still uncertain.
Our boys have never bitten us, we've been nipped in a curious "are you food?" way but never very hard. When they were little they nipped a little harder than was comfortable in this way (never broke skin) but within a couple of weeks they worked out just how hard they could get away with and now they rarely do it.
Getting rats is expensive, the initial layout is expensive bcause you need to buy a lot of toys and hammocks. Hammocks need changing quite regularly, toys need to keep them interested. If you get a wheel for rats you'll be looking at £20+ unless you get one of these:
www.ratrations.com/running-disc-p-1069.html
Whatever you do, do not get something like this:
www.littlepetwarehouse.co.uk/blue-metal-large-28cm-degu-chinchilla-wheel-p-16673.html which is a potential guillotine job waiting to happen (tails can get caught between the wire on the wheel and that of the wheel frame) and never ever get something like this:
www.amazon.co.uk/Rat-Wheel-Cage-Toy/dp/B0037XRU8W/ref=sr_1_5?ie=UTF8&qid=1399805728&sr=8-5&keywords=rat+wheel
Because with that one they can get their feet stuck and rats are prone to a nasty problem called bumblefoot, which can be aggravated by walking/running on mesh.
But rats aren't keen on wheels for the most part according to research I've done on it, some people say that if you introduce it young then they'll use it. Our girls came with one (when we rescued them we got a cage with them with a wheel, both the cage and wheel were unsuitable tbh) and we binned their wheel as soon as they arrived, we did replace it after 6 weeks after a lot of debate (got a 12inch silent spinner for £20-odd) but they rarely use it. One will use it for 20 second bursts and get bored. We don't regret buying it as we'll put it in with our boys when we get another pair but there is no guarantee that they'll enjoy it and it's one of those things that is very expensive for the amount it's used.
Rats need a lot of time out of their cage, recommended time is a minimum of an hour. Our boys free-range for 30 or so minutes a day too, which is allowing them free roaming over a room. You have to rat proof if you are going to do this, as 70 probably remembers, my brand spanking new baby rat got stuck under the fridge before he'd even made it into his cage. I can't find the thread (was in chat so probably gone now) but I was so devastated. Now that they are older they are better around that area and much bigger and we can trust them, whereas we can't trust our girls so they don't get to free-range right now.
Buying online is much cheaper than buying in shops, and you should never trust what a shop says about rats, always do your own research online, there are many great forums for this and I've actually found reddits rat subforum to be brilliant too.
Hammocks are great but can be expensive, there are ways around this (using old t-shirts or fleece) but a few properly made hammocks are nice too. Tubes and other toys can be made out of charity-shop kids trousers.
This girl makes amazing hammocks:
www.rataccessories.co.uk/
Vets bills can get expensive. Our vet is good, when all of ours got URIs they only charged us to see one (they saw two) and trusted our judgement on the other pair and gave us meds for all of them. Rats are prone to URIs, read up on it and find a vet who is experienced with rats. We contacted every vet in a 5 mile radius and ours didn't have anybody experienced particularly in rats, but they had somebody who was a new vet but specialising in small animals (with a particular interest in rodents), two very experienced vets and quite a few of the staff have rats as pets.
Buy a few cheap baggy zip-up tops and jumpers, rats love running around in them and sleeping in them. Ours will dive under our shirts too and sit in my bra. They may chew the clothes though, which is why you should buy cheapy ones. Don't let them run wild in knit-wear, they get their claws stuck and chew it to get loose bitter experience.
Apologies again for the essay! I love rats, they really are lovely pets! But they become very addictive too once you start looking at toys and things! We spend about £60-90 every 6-10 weeks on food in a batch order for four rats (we make up our own mix, much cheaper than buying specific rat food) and probably between £20 and £50 a month on toys and hammocks and things.