There is too much risk in making them known into this currency.
The risk of making their way to porn or to gambling.
So I would rather not teach it to them and let them enjoy their childhood preserving the innocent minds.
There will come a time that they will know about this but not now.
They could play games but not bitcoin games with advertisement that you dont know what will pop out there.
I do not think that children will understand bitcoins to the extent that they understand that these coins can be used in a bad way.
But, I agree with you - the children do not need to know about bitcoin. I do not know why they need it