Such foolish questions.
Consider this:
Believers die just like unbelievers die. It doesn't mean any failure upon an angel.
When a believer dies, where was the guardian angels? The same place they were when Jesus died on the Cross. (Matt. 26:53) "Thinkest thou that I cannot now pray to my Father, and he shall presently give me more than twelve legions of angels?
The 'will of God' is always the deciding factor.
And, what makes you think 'all children' are of God and have a guardian angel? Just because one is a child in the human race, doesn't make him/her a child of God.
Quantrill