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 (سنن أبي داود رقم 4195)

Hazrat ibnu ‘Umar (radhiyallahu ‘anhuma) 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 (سنن أبي داود رقم 4197)

Hazrat ibnu ‘Umar (radhiyallahu ‘anhuma) 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).”