You can assure your nephew that deer attacks are very uncommon, especially towards children. In an interview concerning a recent deer attack in California, Larry Hawkins, a public affair officer for the United States Department of Agriculture, had to go back to 1977 before finding a deer attack on a child, and that was in a National Park (see article).

On the vehicle side of things, meticulous records of vehicle accidents are kept both in the US and elsewhere. A paper published in 2000 noted that data from the National Highway Traffic Safety Administration showed in the previous year there were 231 deer related fatalities in vehicle accidents in the US. So death from a deer running across the road is hundreds if not thousands times as likely as death from direct deer attack, but even this is exceedingly unlikely. From all causes, the chance of being killed by a deer in a given year is less than one in a million.

That being said, deer (outside of petting zoos) are still wild animals, and the advice from the USDA Forestry Service applies: "please do not feed wildlife, and do not approach wildlife. If an animal approaches you...move away and maintain a safe distance."

Mark Huber