Story about seven dimensions fantasy

I'm looking for a book i read in 2009 and it was about three kids who had to travel across seven diffrent worlds and do something. I don't remember much but I remember one of the worlds had a green sun and blue grass and in another world people never left there houses. Advanced technology cared for them and all the had to do was say it out loud and it would appear and they had these vr things and they would go into a simulation game and play with there friends. It looked kind of older and I think there was seven colorful stones in an arch on the cover and I keep wanting to say the title is 'of the seven worlds' or something like that. Please help me!

That sounds at least a bit like the Diadem: Worlds of Magic series by John Peel. The first book is Book of Names.