Which of my grandchildren will go to Hell

I have grandkids of various ages and none are baptised/christened.

At what age are they responsible for their own sins and therefore Hell if they die.

Is it day 1 or year 5 or age 18 or what?

It has been said God has no grandchildren so then each person must make his own decision but then even early Christians baptised their whole families.

If my parents baptised me as an infant do I have a free run ?

This is one of the nonsensical things that make you laugh at the whole idea or salvation.