How old is too young to take pictures of youngsters half dressed?

Basically it comes down to this. My ex married a registerd offender. I found some pictures that she has taken of my daughter who is five out at a river and she is topless in them. I kind of find this a bit disturbing since her husband was put on the list for playing with a minor to begin with. So basically are there any laws regarding this or is this just something done in poor taste. The picture does not appear to be ual, but still in my opinion is that she is a bit too old to be running around without a top on.