1. One should keep the hair of the entire head the same length. It is impermissible to trim the hair in two different lengths.
عن ابن عمر قال نهى رسول الله صلى الله عليه وسلم عن القزع والقزع أن يحلق رأس الصبى فيترك بعض شعره. (ابو داود رقم 4195)
Hazrat ibn Umar (Radhiyallahu Anhu) reports that Rasulullah (Sallallahu Alaihi Wasallam) prohibited qaza’. Qaza’ refers to where a part of the head of a child is shaved and a part is left unshaved.
عن ابن عمر أن النبى صلى الله عليه وسلم رأى صبيا قد حلق بعض شعره وترك بعضه فنهاهم عن ذلك وقال: احلقوه كله أو اتركوه كله (ابو داود رقم 4197)
Hazrat ibn Umar (Radhiyallahu Anhu) reports that on one occasion, Rasulullah (Sallallahu Alaihi Wasallam) saw a child who a part of his head was shaved and a part was left unshaved. Rasulullah (Sallallahu Alaihi Wasallam) prohibited them (the family) from doing this and said: “Either shave all of it (the hair) or leave all of it (as normal while all are even length).”