Bright blood in or after stools could be due to a variety of conditions, the commonest being hemorrhoids(bleeding piles) or anal fissures. Check out if he complains of pain lasting some time after passing motions or hard stools (more likely to be anal fissures in that case). In case of hard stools, give him a diet rich in fibers like green leafy vegetables, fruits, oats and lots of water.
Also get him to consult your family doctor or a surgeon so that they can examine him and diagnose the cause and suggest appropriate remedy. Homeopathy
is beneficial in both the conditions .