Most children will sooner or later be exposed to bad material via the internet. There is much more danger than there was only five to seven years ago. The reason? The explosion of handheld devices. Stationary desktops are going the way of dinosaurs. Too bad. There are all manner of filters available, and one can lock the door. You can see to it that YOUR child doesn't have an iPhone, smart phone, android, tablet, but you can't prevent someone else's child from having one. Children as young as three or four know how to operate these devices. I've seen groups of lower elementary school children clustered around an iPad after Mass. In one instance they were watching one of the children's classmates "perform" --lip-synch and dance (gyrate while scantily clad)--to a Justin Bieber song on YouTube. Don't assume your child is "safe" or has "preserved his innocence" just because you go to the Latin Mass, have your computer locked up or don't have one, or a TV, or a radio, and only a landline phone in your home, and you exclusively home school. Short of locking your child in an underground bunker until he is 21, the best parents can do is to make sure what is done in YOUR home, by YOU exemplifies the home life of the Holy Family. Steep your children in Truth, Charity, Purity so that when they encounter the opposite, they will recognize it as the work of Satan, and possess such love of truth so as to despise it. AND...These are the most difficult because they come only by prayer...Pray for fortitude in your child to be the one who says in front of his peers, "That's nasty. Let's not watch anything so displeasing to our Blessed Mother," and walks away, hopefully with other weaker souls following. AND...Again, difficult in today's world where there is a constant undercurrent against charity and authority, pray for and create the kind of relationship with your child wherein he will come trustingly to you when he is exposed to the world's filth, and not feel he must 'keep secrets' out of fear and shame that you will blame him for having had his eyes and heart defiled.
The solution is not in having the right technology, for that constantly changes. The solution is to limit, in as much as possible, very young children's access to technology, and to build up their souls to the point where they will install the filter of the never-changing, 100% effective Holy Ghost in their hearts and minds.