I would go with guinea pigs, they are very placid calm creatures. DD (6) has 2 females who live in her bedroom. Ours are indoor piggies but they do go out in a run in the garden on nice days.
They do need to be cleaned out every 2/3 days and ideally need daily handling/interaction as they can be shy and nervous. Guineas rarely bite and so you shouldn't get the nips that you would from a hamster or gerbil when you are taming them. Guineas need to have a good sized cage or hutch, please don't buy a pokey one, even if it says 'suitable for guinea pigs' on it. Proper sized guinea homes can be expensive and large so you need to take that into consideration.
Indoor piggies are generally tamer than outdoor, just because they have more regular human interaction. I would advise against getting long haired pigs if you are a first timer as they take a lot of grooming.
Also please buy a pair of pigs as they get very lonely if kept singly.
In short I would advise you getting a pair of smooth coated/short haired females (pairs of males can often fight females do not tend to).
The lifespan of a guinea is 5-9 years (indoor ones tend to live longer because they are not exposed to the extremes of temperature that those kept outdoors are), so take that into consideration also.
If you do decide to get a pair of piggies then do get a good guinea pig care book too, it gives you alsorts of helpful tips.
Guineas can be trained to do 'tricks' but are also equally happy being snuggled up on your lap watching tv.
This is the set up I have for my pigs...
Cage. Ours is on the stand shown to keep it off the floor (away from draughts and vibrations). I took the yellow hide platform out of mine as it kept collapsing if one of the pigs stood on the top of it.
Houses. Ours have one each so they can get a bit of peace if the other one is being annoying! These replaced the yellow hide/platform.
Hay manger The cage came with a yellow one which fitted to the ouisde of the cage but it made a mess of the carpet around the cage so I bought this ball which can be hung from the roof of the cage and the mess is greatly reduced.
Outdoor run
This is a helpful PDF helpsheet on guinea pigs