@DoorOpening
I haven't kept rats , my rodents were non-tailey, non climbing, not very bright guinea-pigs (but I loved them !
There's a tonne of good advice on Small Pets , search up rats in this section.
First thing you need to decide is their accomodation. Size of cage , where will you site it , what enrichment will you supply in their
Then somewhere safe they can explore , they are active little things . You can train them to respond to their names , they're often described as being like tiny dogs .
Boys or Girls ? Boys are heftier but considered friendlier .
You need a good Vet who is RatSavvy and read up on their dietry needs and ailments . They are respiratory sensitive and can be prone to tumours .
You are right to stay clear of P@H , factory farming for rodents 
Rescue rats might work but you need to know what you're getting ( All my guinea-pigs were from Rescue and some quite sad tales how they ended up there for some , not all . None of it was their fault so they didn't have behavioural problems , just not good starts for some of them)
Like all animals , keeping them clean ( I recommend steam cleaners as its just water ) and hand hygiene .
Some keepers recommend three as inevitably one dies and they need company . Your DD and everyone else in the house needs to make sure there's no allergies to the fur or any bedding they use .
If she wants rats in particular then get her to research .
Good Luck !