What worries me is that so many young people are growing up without any real knowledge of God,
No such thing, unless you can provide a means of somebody else sharing the thing that you miscall knowledge. There's certainly
knowledge of beliefs about God, but there are squillions of those. That's what religious education is for, to teach the basics of the main ones.
Regardless of this point, why does this worry you if,
as you claim, you're quite happy for people to make up their own minds? What are you worried about?
I recently came across a statistic which showed that a substantial percentage of children (I can't remember the exact figure) did not know why we celebrate Christmas.
What you actually mean here of course is that they don't know why
Christians (which chances are they will not be) celebrate Christmas. For the rest of us it's a jolly public holiday, a winter festival - time off school for them, time off work for mum and dad, presents, lots of nice food, etc. etc.