Intellact levelof my child not accto age

Good evening doctor. My child is 6 yrs. The problem of my child is that his intellect level is not according to his age it's like when he is in a class whenever teacher write on a board he is not able to write even a single letter in notebook write now he is in ukg. Similarly when she say take out Hindi notebook from bag he doesn't get it what she says and does not respond.when he goes for play outside he used to play alone generally he does not understand what other are playing. He enjoy with himself and remain discarded from others children.morever he is not able to speak fluenlty able to speak 1 to 2 sentences.He is very active child not sit idle even for a second.being a mother when I taught him initially he takes lot of time than he open notebook.does not pay attention while studying . Kindly help me I am very confused whom I need to concern. Principal of school give me last warning next year she may not promote him for next class. Thanks