In Esther Rabbah, a story is recounted about the threat that Jewish children posed to Haman-Amalek:
When Haman and his accomplices saw that Mordechai was looking for the Jewish children, they pursued Mordechai to find out what he was asking them. When Mordechai reached the children, he asked of one of them: Tell me a pasuk (verse). The first responded:
אל תירא מפחד פתאום ומשואת רשעים כי תבוא
Do not fear sudden terror, nor the havoc of the wicked when it comes (Ecclesiastes 3)
The second continued: I read this today in school:
עצו עצה ותופר דברו דבר ולא יקום כי עמנו אל
Contrive a scheme, but it will be foiled; conspire a plot, but it will not materialize, for G-d is with us (Isaiah 8)
The third said:
ועד זקנה אני הוא ועד שיבה אני אסבול אני עשיתי ואני אשא אני אסבול ואמלט
Until your old age I am [with you]; until your elderly years I will sustain you; I have made you, and I will carry you; I will sustain you and deliver you (Isaiah 46)
When Mordechai heard this, he laughed and had great joy. Haman said to Mordechai: What is this joy that you have at the children's words? Mordechai responded: On the good news that they reported, that I shall not fear the evil schemes you scheme against us. Immediately Haman was infuriated and said: I will strike these children first.
Rav Mordechai Elon, in his booklet Techelet Mordechai on Parashat Vayikra says:(Esther Rabba, 7)
The breath of the these schoolchildren is what frightens Haman. Their pure and holy breath, ripe with emunah and bitcahon, manages to awaken his rage and upset his ease. He too, deep inside, senses their power and their emunah, the great joy of the three children who are bound to the Eternal and read their pesukim.
On Shabbat Vayikra, which marks the parsha that children begin to study Torah, three children were murdered in the hands of our present-day Haman-Amalek.
Haman-Amalek knows our great power and where it originates, but the holy utterances of the children stands true: Contrive a scheme, but it will be foiled; conspire a plot, but it will not materialize, for G-d is with us.
May the souls of Yoav, Elad, and Hadas, the three children stabbed to death on Friday night, be bound in the bond of everlasting life, along with their parents, Udi and Ruth. Tehiyeh Zichram Baruch la'ad.
Also, listen to the amazing response of Chaim Fogel, father of Ruth Fogel z"l, to the tragedy (via Israel Matzav)