I was debating showing Eps 4-6 to my daughter this summer (she's 5.5). I really want to watch them with her but I don't want to scare her. I definitely think episode 3 is too scary.
I didn't show my son Ep 4 till he was 6, (he's seven now and has seen 4,5,6 & 1 - in that order) that said you could cover her eyes just at the scene where Luke finds his Uncle and Aunty after stormtroopers have visited, that's what I did

. It was great watching with him, but I didn't want his first Star Wars experience to be the new episodes. I'm one of those dudes who saw Star Wars at it's premier in 77, a really wondrous experience. You know, I share the disappointment of fans in the new episodes, but there is much technically that can be credited to Lucas that we enjoy today in both home cinema and cinema. From Star Wars came (essentially) much improved multi channel sound systems, the technology eventually found it's way into our homes. The flips side of the coin is that the great era of creative control by directors (70's) ended with Star Wars and Jaws, with the blockbuster came the "who cares what it's about as long as the kids go" ruling mentality in Hollywood at least.
The irony is that Lucas exerts total 'creative' control over his films now and turns out empty dross as a result. For anyone interested a great read about the topic (including) Lucas's and others story is the book "Easy Riders Raging Bulls by Peter Biskind".