Let children be children
Because childhood should be childhood; because there is a time and a place and a person from which to find out some things; because childhood should be full of fun and games and make-believe and learning; because the Internet is full of fun and games and make-believe and knowledge, and is a great place to learn all sorts ofthings; and because the Internet is also full of things you should not find out about or encounter until you are older. Not just adult things, older things; there are things you should learn when you are seven or eight that you are best not knowing when you are four, and things that are best not learnt when you are seven or eight, that are for when you are ten or eleven, or for the teenage years or later.
And because every child is different, and because you know your children; you choose to let them believe in fairytales and (sadly) when not; you choose to shield them from some truths (and maintain some lies!) until they are, in your judgement, ready. We cannot control who else tells them things before you think they are ready, but we can help you control when they encounter those things on the Internet.
Because it is not about adult or not, it is about child or not.