bit of a silly uneducated post really,
koran is much much smaller than the guru granth sahib, in addition to this they can read it in english, its not exactly mandatory for all young muslims to learn arabic, whereas the earnest on gurbani is to learn punjabi and gurmukhi, all in all its much harder to read guru granth sahib ji than it is for kids to read koran
im sure you would see a massive incread in numbers if every kid were to read guru granth sahib in english, but this clearly isnt the case and it shouldnt be either, children should learn gurmukhi and understand the true meaning rather than settling for second best translation