The childrens parents made the choice to bring them, and I can't see why this would in any way be harmful to them. They'll find it gross and interesting. Children are far less fragile than adults give them credit for. The Zoo did what the had to do to keep the gene pool clean. This happens a lot when managing animals, it's necessary to keep Zoo's functioning and in the long run have healthy animals. It's a responsible rational decision, just like any farmer would do.
Debate the necessity of Zoo's, instead of misunderstanding basic animal keeping.
Hell, how many healthy animals get killed everyday for no other purpose than to become food for obese humans? As far as captive animals go, Eugene the Giraffe had a good short and meaningful life.