We tend to pray for the things that we want and the people we like. While this is not objectivity wrong, we should challenge ourselves to remain vigilant in asking God’s will and consider who needs our prayers the most, regardless of our feelings. In this way we can ensure our prayer life is not linked to our own selfishness.
Consider it like “fasting” from our favorite and most comfortable prayers to try a narrower path. I’ve heard it said that it is impossible to truly hate someone if you pray regularly for that person. Try it sometime as an act of the will. Of course, we should pray for all the victims too, who include the mothers as well as the children, but this is not very challenging to do. Prayer for the killer is uncomfortable, but being comfortable is not what Jesus promised us and is not the purpose of our life. I’ve also heard it said that a good Catholic will make many people feel uncomfortable.