yes constantly
The other day i saw a little girl fall off form her bike, she had pretty badly skinned her knee and was crying pretty bad.
I wanted to help her, but didnt because of exatly this.

I have friends who say they would NEVER approach what they thought was a lost child, because of this.
If I saw a small child walking in the street alone, I have no idea what I would do.

I saw a video with John Stossel or somebody that had a child actor crying alone on a street corner.
Out of hundreds of people who passed by her, only one elderly lady stopped to ask her where her parents were. The males who were interviewed stated that they didn't want to help the child for fear of being labeled a paedophile.

I saw a lost child in a museum once but simply told a guard and then later when I saw the family I told the family I told a guard.
There was no way I would have taken the child by the hand to find a guard like would have been rather common several years ago.