For young children it may be better to invest in something more age appropriate that can be adapted as the children mature. The Nabi Tablet is an example. It has a password protected parent-mode (fully funtioning tablet) and a child-mode (approved content only).
I assume you are responding to me. No, I am not kidding. I do, and have allowed my kids access to all this. Just not unfettered access. Far be from me to tell one how to raise their progeny, but if that's what you want for your child, fine. My concerns are for children who are not well rounded and I'm not referring to their physique which of course can be seriously compromised due to a lack of 'play'. There is plenty of time in life for people to get into computers, the Internet and all that. There just needs to be a healthy balance, and parents are the ones responsible for setting limits, ensuring balance. I certainly hope your four year old turns out to be a well-adjusted productive citizen. That's what we all want for our kids. My youngest of four children is now a junior in high school. I know a little about what happens in the teenage years. Brace yourself.
Perhaps, YouTube should allow viwers to rate the videos and then build a filter on the player. There's far more education/entertainment on YouTube than the 'bad stuff'. If you don't allow your 'kids' on it, then they'll missed out. My four year old is learning spanish on YouTube.
My two young girls aged 2 and 4, loves to watch kids stuff on youtube. Mostly this works out fine, as they get suggestions for other kid stuff to watch. This is very helpful to get the kids to learn letters, reading and singing (well, mostly in english. There isnt so much fun in our native language)
But Ive learned to be careful. Once youtube linked to episodes of "happy tree friends" where I had to brutally remove the pad and flag as inappropriate (if you don't know the series, have a peek, its pretty ugly cartoon stuff) Tbh, I don't know how a 2year old would react to this, but the tiniest thing like this wobbling space clock in this episode of professor Baltazar at 5:35 made her really scared this weekend.
Of course you can't prevent kids from being scared, you just need to be there to explain whats going on.
And then of course, as they get older, there are other challenges..
A PC for children's use can (and should) be parked in a "public" area such as a family room, where parents and siblings are roaming. No privacy? Yep, that's the idea. I want to know what you're doing. iStuff is too portable to young ones. Once they have been taught responsibility and gained sufficient trust (agreeing with a comment above) then the strings can be loosened and the iGadgets can be theirs. "All my friends have them" isn't good enough. As parents, our job is to occasionally be the meany that protects and teaches the child.
That is the best way to be a good parent - educate your kids, and trust them. (There are occasional exceptions, as always.) Protect them from accidents and things outside their control, but your job is to teach them to keep themselves safe - not to "nanny" them until they leave home.
When they are younger, you are with them whenever they are using the internet. As they get older, you teach them how to use it safely, you teach them about "good" sites and "bad" sites, and what to do if they accidentally get to a "bad" site. And you gradually move more into the background.
As they get older, you get less involved in what they are doing on the internet (but make occasional spot-checks), and your discussions and lessons about "good" and "bad" cover new topics for older kids.
And sure, they will stretch the boundaries on occasion. You want to have enough control to stop things getting too far - but "experimenting" is an essential part of growing up.
It's not really very different from other "risky" activities in a kid's life as they grow up, such as cycling, driving, alchohol, going out with friends, etc.
Parents should not let kids use PCs unsupervised until they are old enough to use them safely. And "safe" in this context means that they are responsible about what they read, watch, write and publish on the internet, that they treat other people's data responsibly and respectfully, that they understand how to avoid malware, and that they understand clear rules about what they can and cannot do on the PC.
Until that is in place, then the kid should not have access to a PC, Pad, "smart" telephone, or similar devices without supervision.
Call me a Luddite, but it's high time kids learned how to play with things without transistors. I've seen far too many young people who are computer and technology saavy but are dumb as rocks. They have no clue as to the real world because they have not experienced it first hand. PC usage needs to controlled closely.
If you want to know where I am coming from, John Rosemond writes an excellent column on common(?)-sense parenting. He basically turns all the psycho-babble parenting techniques on their head. I encourage you to read his work. We as a society have done the last two generations of children a terrible disservice.