Can't believe this hasn't been said yet, but pretty much any of the Katamari games should be perfect. While I've only played the first two, here's what I can say gives them a huge advantage for kids in my book.
1: Lots of bright colors, fun noises, silly stuff, and just generally a lot of different things to look at. Every level is full of bizarre things like dancing flowers, batteries rolling around, toys that bounce at you, just any kind of crazy thing that is bound to make kids grin. Additionally, the Royal Rainbow is enough for any kid.
2: Very simple gameplay with very easy to understand tutorials. While she may have to read slightly, the intro usually shows exactly how to move the sticks to make your character roll the Katamari. The only thing she might not get is the charge move where you jiggle both sticks back and forth, but it's not really ESSENTIAL to gameplay, just helpful sometimes.
3: Usually the goals are very lax, it's fairly easy to reach the required size (or whatever the goal is) in time, and if you really want to make it easy, finish the game first and let her play with time limits off. (I can't remember exactly how that works or if it's available all the time though, I just remember I could do it in the first game).
I think the game can be very engaging and simple to learn. The only real concern is, if she can read well, sometimes the king's response MIGHT be a little discouraging on occasion. Unless you're in the top tier of scores he can be a little mean at the size of the Katamari, but it's usually fairly lighthearted and no doubt kids would be able to shrug it off fairly easily. Otherwise there's Katamari Forever for PS3 and Beautiful Katamari for XBox 360.
If you have a PS2 (or backwards compatible PS3) I'd recommend We Love Katamari, as it has the best levels, as well as most variety of levels, and a really good tutorial. Also, it's my personal favorite. Otherwise, there's Katamari Forever for PS3 and Beautiful Katamari for XBox 360.
Additionally, Pokemon is a great starter as well if you think she might get into RPG type games. The cute style, inability to die and ability to rename pokemon, as well as having a large variety to capture should keep any kid engaged, and when they get better there's a pretty good RPG system behind it as well. Of course, if they start off not being that great AND they get bored of grinding easily, it might not keep their interest all that long.
EDIT: it cut off a bunch of what I wrote. Weird. Edited to finish it off.