I own pretty much every DVD there is so far of the Transformers Prime series, and love every minute of it. It's also a winner with kids! It has far more "dark" themes than the likes of Rescue Bots or Generation 1, but that hasn't stopped my friends 9 year old son enjoying this series! If anything, he loves this show more than any other he's seen.
I would still recommend a parent watch any of the Prime series should there be children below the age of 9 viewing it, not exactly for the themes of peril and robot violence, but more so to help them understand what's going on better; the show talks in a far more mature tone, and some plot-points have been difficult for my friends son to understand without me being there to explain it all to him in a way that he understands.
So it's a great series, if a bit complicated and dark for young children; this show is definitely better suited to the more mature fans of the franchise.
If in doubt that your little one can view this series comfortably, why not try Rescue Bots instead?