Why? The Bible states people have free will, even to do evil. God did not let these kids get murdered if that is the case.
The Bible states people have free will,
Cite?
"Most assuredly, I say to you, whoever commits sin is a slave to sin. - Jesus Christ (Jn 8:34)
"Therefore do not let sin reign in your mortal body, that you should obey it in its lusts." - St Paul (Rom 6:12-13)
To say one has free will is to call Jesus Christ a liar, and to categorically reject Romans 6-7.
There is evil because the carnal man loves his sin and only desires to engage in even more sin (Romans 1)