At what age is a child responsible to their diety?

In answer to your initial question; none, deity is responsible to the children of their faith. For your second question (which is a bit on the silly side); the answer is simple, they all do. Questions like this are like some kind of psychological test. The way you answer it, speaks to your personal character, prejudices, and morality. Why do you ask anyway?

The age of reason is around 11 or 12

This is when they usually give up make believe & Santa.

It's different for every child, just as when they learn to walk varies depending on the maturity of the kid ... but on average, it's around 8 or 9 years of age when they are capable of understanding.

Adults are man kind when they put away childish things: laws.

Until then, their words and actions are considered as adult-ery.

Spiritual adult-ery is claiming to be espoused to grace & truth,

then found still whoring with laws & lies, such as Christmas.

As for the free pass of grace, all is neither many nor few.

Grace --> Mercy --> Peace to all, not some only.

it doesn't matter, because a bus full of children is dead. It's just tragic and unfortunate. To sit and speculate about which ones you think will or won't be cursed for eternity seems really messed up.

The age of reason -- around seven years old.

http://www2.scholastic.com/browse/article.jsp?id=7...

http://www.research.umn.edu/irb/faq/children.cfm

At whatever age they start understanding and believing in something.

After puberty or After having your first "wet dream" your are responsible, but thats just the view for Islam.

As soon as they can recognize good and bad.