House sparrows and starlings are aggressive and will actually destroy and dump eggs from a bluebird nest and kill both young and adult birds when encountered. Monitor nest boxes closely and remove sparrow and starling nests immediately upon initiation. To see pictures of these unwanted birds click here . Female bluebirds may sit quietly on the nest as the door is opened. In this case, close the door and return later.
Bluebirds are very tolerable of humans.
All birds have a poorly developed sense of smell and touching around the box, eggs or birds will not cause the bird to abandon the nest. All of this is part of the enjoyment and learning associated with a bluebird trail. The One-Board Box shown below makes for a nice nest box. It's easy to build and maintain. This would be a good nest box to build with your child.