True what Clint says ... Any small-ish child gets within a few feet of you, you wont see and is why most Troopers have "Handlers" .. My wife ( who was my handler this past weekend ) did a lot of "subtlety" getting my attention to direct me towards a child that i could not see.
Another point is .. You can see more when you ONLY have your helmet on ... once you put your chest plate on .. the range of motion you head has changes.