Another interpretation of "And He shook out [va-yena'er]": He handed these over into the hands of tender angels [mal'akhim ne'arim] and these over into the hands of cruel angels, as it is said, "And a cruel messenger shall be sent against him" (Proverbs 17:11); "Their soul dies in youth [ba-no'ar]" (Job 36:14), and so on.
The Egyptians Handed to Tender and Cruel Angels
Yalkut Shimoni on Torah 237:2
דָּבָר אַחֵר וַיְנַעֵר, מָסַר אֵלּוּ בִּידֵי מַלְאָכִים נְעָרִים וְאֵלּוּ בִּידֵי מַלְאָכִים אַכְזָרִים, שֶׁנֶּאֱמַר "וּמַלְאָךְ אַכְזָרִי יְשֻׁלַּח בּוֹ", (איוב לו, יד) "תָּמֹת בַּנֹּעַר נַפְשָׁם" וְגוֹ'.