Rats are brilliant, I'd say especially for kids too. We have 6 and three of them are from a brilliant nfrs breeder who has very family friendly rats. Theyre very happy to be handled by children, what sold me was when I was at her shop (she runs a pet shop too) and playing with the babies she had in her 5/6yo daughter was there and picking the rats up, handing them to me, taking them back, etc and the rats were completely unphased. So a good breeder is essential. If you're near Brighton I can highly recommend mine! I know people travel from quite a distance to get rats from her too.
They need a lot of time with their humans though, you need at least a pair though I'd say ideally three. Lone rats are generally not happy rats. We have one as he can't be socialised due to health issues and he takes a lot of work, he's out for at least 5hrs a day 5 days a week, usually longer. If he were like the others that wouldn't be enough time IMO. Our others are out for around an hour a day.
They are prone to respiratory problems so you need to find a vet with rodent experience, preferably a rodentologist. Saying that, only two of mine ever really get respi issues that are bad enough to see the vet with and they have them constantly. Ironically the only rat who has never seen a vet is our rescue who we think was originally from a pet shop!
Females are prone to tumours too, usually they are "harmless" until they get very big and hinder the rat but you need to be prepared for that, we lost our rescue girls sister to tumours last August as hers was cystic and eventually it burst bad enough that she had to be pts. We had our two younger girls spayed which drastically reduces the risk of tumours, however ops in rats carries risks in itself and its a very personal decision.
I'd advise having money aside for rats in case of emergency too, we have £300 stashed at all times. Its a bit much but it'd cover three emergencies that needed ops in any given month! Its £50 per rat really. We've only ever had one emergency but I'm paranoid 
I wouldn't advise pet shop rats or rescues as your first pair, they can be hard work! Definitely well bred and handled ones.
After saying all that, I really do think they're awesome pets and great for kids :) I love my mischief! I wouldn't advise having three cages though, that's not fun ;)