I can happily say that there are easy ways to control children on PC. I mean seriously you can set-up passwords for
[u]everything[/u] on PC.
Consoles, not as much, and even less so with Iphones/Ipad/(<--Same things guys-->)Tablets.
The last three are meant to be personal objects, they aren't meant to make it hard for common use. And if your child has any of their own Iphone/Ipad/Tablet (or you're not around while they use yours) and you're concerned about keeping them safe from things on there internet, then why the hell do they have one of these things anywhere near them.
As for;
Is it safe for 9-year-old kids to play on PC, or would it be better if they played on xbox?
9 year olds are KNOWN for tantrums, do you want your kid chucking a $10 keyboard/mouse or a $60+ controller. Or would you like it that the kid grabs the actual XBOX that is made for portablity, while PC's aren't, and slamming that down when they don't get their way. (Unless its a laptop, then... Have fun, I know I had a tantrum once and accidently broke one of my Father's lappy.)
There was a really good quote along the lines of "Expect wonders from your children, good and bad. If you think, 'No, my child would never throw that $100 toy out the window', prepared to be in wonder."
It's in my textbook somewhere, and I don't wanna study to get the exact quote for you guys.