Why are they called "Ne'arim Ketanim"?
Rashi (from Sotah 46b): They were Menu'arim (shaken out, i.e. empty) of Mitzvos. Radak - they are called Ketanim, for they were Katan (had little) Emunah 1 .
Radak: Sometimes adults are called Ne'arim. These were minors. The same applies to "va'Na'ar Katan Imo" (Shmuel I, 20:35).
What is the meaning of "va'Yiskalsu"?
Radak: They mocked him and verbally disgraced him. Malbim - refer to 2:23:3:2.
What is the meaning of "Ale Kere'ach"?
Rashi: Go from him - you made the place 'bald' for us (without income). Until now, we were hired to bring water from far places. Now our income was lost!
Radak: Elisha was Kare'ach (bald). Malbim - they knew that he was appointed in place of Eliyahu. Amidst their disdain for Nevu'ah and Nevi'im, they said 'how can you be in place of your Rebbi? He was hairy, and you are bald! How can you reach his level? Your nature is opposite to his! Beis Kel was the place of [one of the golden] calves; their fathers taught them to mock Nevi'ei Hashem.
Malbim: They said mockingly, go to Shamayim, you bald one, like your hairy Rebbi went to Shamayim!