This incident took place recently in Halab, Syria. The two years old kid was playing with his father's (33 years old) gun when he accidently fired a bullet hitting the father in the heart and killing him immediately (according to the resources).
See the clip..
Always keep your attention on your child particularly if they are under 10 years of age - this is not an occasional glance while reading the newspaper.
No matter how old your child is you should check on them on a regular basis. The younger the child the more often you should check and if they are under 5 years of age you should never leave their presence.