That is odd
I presume he was charged with causing death by dangerous driving - the *starting point* for this offence should be 12 months to 2 years
http://en.wikipedia.o..._by_dangerous_driving
Unless he was charged with the newer offences of causing death by careless driving - without more details it is hard to say.
Comparing this with theft isn't really a good example - because there is the issue of intent. A thief doesn't accidently steal money nor did this person deliberately kill a child.
A long prison sentence is unlikely to deter others in crimes where there is no intent and this person is presumably not a danger to the community