My cousins, girls 8 and 6, and boy 3 saw TFA in the theaters, 3x.
They have not yet seen the other movies. But with the connections to the OT characters their parents think they will see 4 5 & 6 next.
I think that's about right.
I also read that Natalie Portman showed her 4 year old son no movies yet. Or he is seeing 4 5 & 6 & 7. Because Padme dies in The prequels, Natalie says she doesn't want to show this to her son. Not yet anyway.