Prevention is better than cure. Avoid extreme temperatures e.g. avoid taking the child to extreme heat or keeping in an air conditioned room. It is often caused by dry climate. If the baby is susceptible to nasal bleed then place a pillow under his shoulder while sleeping.
In case the bleeding starts, make the baby sit up straight and make sure the baby is not lying on his back during bleeding. Pinch the nose. Give a cold shower, if shower is not possible then pour cold water over his head.
Also in order to rule out other causes (blood clotting disorders), get him checked by a Pediatrician.