What pet do you want to look after because - no disrespect to your daughters- it'll fall on your shoulders. How old are your DDs How much space do you have for cages? Are there any allergies you need to think about?
How much time and money do you see yourself parting with?
I've had mice and guinea-pigs. Both lovely in their own way but disadvantages with both.
We have a Syrian hamster. He's now three and has been handled by the children most days since we got him around 8wks I think it was. He's a character. Very friendly. Doesn't bite. Has even been known to "watch a movie" sitting on a knee , loves titbits and will happily take from your hand. Easy to clean, both children take care of all that side of things under supervision of course. I wouldn't hesitate to get another one, although we hope not for a good while yet.
Rats are very rewarding. You can train them to do tricks and they're a bit bigger / more robust than some other small furries. Pick a breeder carefully: they are prone to respiratory problems and the females to mammary cancer.
Rats! Rats are brilliant pets and so cute and cuddly. Live in pairs or more too but need decent sized cages and stimulation. They are quite intelligent too and can be taught tricks, all of ours come running to the door when we open it, none are nippy anymore (one of our girls was but she was a rescue).
They really are lovely, if you're near Brighton I can recommend an amazing breeder, three of my seven are from her and they're lovely squishy, handleable and playful creatures.
The downsides are that they are prone to respiratory issues so you need a vet with a rodentologist or somebody experienced with rodents nearby.
Females are prone to tumours. Breeders can be few and far between and have long waiting lists, though if you aren't picky you may not have to wait, that's how we got our two girls as one is brown (agouti) and the other black, common colours for rats so despite the black being a rex (curly furred) she wasn't reserved.
We have had two gerbils for a few months now and they're great! They haven't bitten us but have 'nibbled' a couple of times when sniffing our hands to get used to us. Didn't hurt and they only did it to investigate us. They aren't really sit-on-your-knee-for-a-cuddle pets but they are very entertaining.
They love to burrow and are always rearranging their cage. You will never fill the cardboard recycling again as they love to destroy cardboard.
My two dds (3 and 6) love to watch them.
Also they are pretty clean and don't smell. They are desert animals so don't wee much and they will use a litter tray! (Tiny dish with chinchilla sand in)
Do get the biggest tank you can though. We got the largest Pets at Home sell but they kick out wood chippings through the bars. We are going to invest in a bigger aquarium type tank instead so they can have more to burrow in without spreading it all Over my house!