The real reason is simple:
The mere presence of the Hebrew children are a “proof” to the world that there IS a God, and that He will fulfil His promise He gave to Abraham.
/\ This.
Any Jew's existence, no matter how assimilated is a sign of this. Even an "apostate" Jews's "apostasy" is a sign of the rejection of God's agreement with Abraham, so even they are a sign of the one, true God.
So just the existence of any Jew sticks in the craw of the truly wicked.