My 6 month old baby can’t roll over fully. Whenever he turn he is not able to pull out his another arm out So I help to bring that arm out. With both arms he lift his head for a while and then just lying down on his tummy and take a pause. Then again for 1-2 sec he hold is head up. He doesn’t like tummy time. How can I improve his tummy time?? And could it cause a delay in his sitting also?