DP and I have rats, 6 of them in three cages (two boys, three girls and a lone boy). I'd say that they make fantastic pets for children, especially when got from a family friendly breeder (can recommend an NFRS one in Brighton! It's well worth travelling to get them from a good breeder IMO)
They need very big cages though. And they really shouldn't be lone pets, they need company of their own kind. You get the rare one who can't integrate with it's own kind, but they really are rare and require a lot of time and attention from their human.
We have this cage for our pair and trio:
www.littlepetwarehouse.co.uk/hamberley-single-metal-large-cage-p-12607.html
Rats need height to climb so aviaries are quite good and a cheaper option than specialist cages. We needed all metal as our girls chewed through plastic bases, so we got the hamberley for our girls and liked it so much we got it for our boys too 
Rats are lovely pets, and, IMO, very good for children. Well bred rats don't tend to bite, they'll nip at first a bit like a toddler would use their mouths to explore things, so it's worth knowing so that you're prepared, but they don't nip hard and if it's too hard for you you can 'train' them not to do it too hard. One of our 5mo girls still nips when she wants to play chase with you, it's quite sweet actually!
You need a good vet though, rats are prone to respiratory infections and a standard vet won't always pick up on it. We visit the vet about once a month, usually with one of our boys who has bad lungs so constantly has respiratory infections! We see a rodentologist and I cannot fault her., it costs us just under £30 a trip for the consultation and medication. OPs usually cost under £100 at our practice for rats, though it varies. Our two young girls were spayed and that was £60 each, when Howl had his eye out it was around £100 IIRC and that included an emergency vet visit.
Rats are lovely though, all of ours have different personalities and even our rescue who died of a tumour in August and was utterly terrified of being out of the cage (and us at first) was lovely and rewarding!